I own a copy of this lens. Great lens. Use it a lot. I strongly suspect, as have others before me, it's the zoom lock that you are engaging accidentally (although it surprises me a bit you could get the zoom to move at all with the lock engaged). Some folks like this new feature and others do not. The following is from one of the many reviews of this lens I found on-line.

"See Flex Zoom Lock

One of the major updates present is the “Flex Zoom Lock” mechanism.
This is a furtherance of the traditional zoom lock switch available on many high-end telephoto lenses. Instead of using the zoom lock switch as usual, the photographer now has the option to lock in at any at any zoom range simply by sliding the entire zoom ring forward. This not only saves time but also ensures the photographer can intuitively lock zoom without breaking eye contact with the subject."

Well, I've been hemmin' and hawin' about getting a longer reach quality telephoto for use with both my EOS R and T6s than my old Canon 70-200mm 1:c.8 L IS USM bought used last year. Even with the second hand 1.2x and 2x Canon Extenders, the reach isn't super, and as some here had cautioned, with the 2x image quality suffers a bit.

When I bought my R, I tested a Tamron 100-400 - and a Tamron tech present for Mike's tent sale even performed a firmware update onsite - but AF performance was dismal. So, I had settled on either getting an old Canon 100-400mm with IS or Tamron's 150-600 G2, which was said to perform well with the R. Now, I see on Tamron's website that version 1 AND the 100-400 are claimed to be "Usable after firmware update." Now that I've received a used G2 (rated EX) from KEH, I can confirm that it works just dandy with the R, and I'll attach a couple of backyard photos as evidence. [Following is a short story to go with the photos.]

I've been watching various sources for a suitable deal on a G2, and almost pulled the trigger on one at KEH rated BARGAIN. Dallied, missed, then this EX popped up, I talked it over with the spouse, and made the leap. It didn't hurt that KEH is offering a full year warranty on anything sold in Nov and Dec!

I took the lens out with both cameras on a dim gray day yesterday to try it out, and it worked fine. Until just before I headed home, when the zoom ring got really stiff. It was fairly cold, but only in the 40s, so I thought that shouldn't be a problem. In the backyard today, it was still stiff...until suddenly it wasn't. I had intended to call KEH today and warn them the lens might be coming back. Now I'm unsure. I'm thinking maybe I should just send them an email to describe what happened and warn them I may end up returning the lens. Then wait and see.

What do you think?

Anyway, the story on my sample freehand shots here...again, a really gray day (excuse up front): there were 5 squirrels in the row of trees at the back of our yard, an unusually large gathering. One looks black from a distance. This one dark squirrel kept chasing 3 squirrels away while alternately separating the 5 squirrel in a different direction. That strategy's purpose became clear as he eventually had his way with her while the other 3 looked on from a distance. He's a very distinctive sort of squirrel, methinks.

Well, I've been hemmin' and hawin' about getting a longer reach quality telephoto for use with both my EOS R and T6s than my old Canon 70-200mm 1:c.8 L IS USM bought used last year. Even with the second hand 1.2x and 2x Canon Extenders, the reach isn't super, and as some here had cautioned, with the 2x image quality suffers a bit.

When I bought my R, I tested a Tamron 100-400 - and a Tamron tech present for Mike's tent sale even performed a firmware update onsite - but AF performance was dismal. So, I had settled on either getting an old Canon 100-400mm with IS or Tamron's 150-600 G2, which was said to perform well with the R. Now, I see on Tamron's website that version 1 AND the 100-400 are claimed to be "Usable after firmware update." Now that I've received a used G2 (rated EX) from KEH, I can confirm that it works just dandy with the R, and I'll attach a couple of backyard photos as evidence. [Following is a short story to go with the photos.]

I've been watching various sources for a suitable deal on a G2, and almost pulled the trigger on one at KEH rated BARGAIN. Dallied, missed, then this EX popped up, I talked it over with the spouse, and made the leap. It didn't hurt that KEH is offering a full year warranty on anything sold in Nov and Dec!

I took the lens out with both cameras on a dim gray day yesterday to try it out, and it worked fine. Until just before I headed home, when the zoom ring got really stiff. It was fairly cold, but only in the 40s, so I thought that shouldn't be a problem. In the backyard today, it was still stiff...until suddenly it wasn't. I had intended to call KEH today and warn them the lens might be coming back. Now I'm unsure. I'm thinking maybe I should just send them an email to describe what happened and warn them I may end up returning the lens. Then wait and see.

What do you think?

Anyway, the story on my sample freehand shots here...again, a really gray day (excuse up front): there were 5 squirrels in the row of trees at the back of our yard, an unusually large gathering. One looks black from a distance. This one dark squirrel kept chasing 3 squirrels away while alternately separating the 5 squirrel in a different direction. That strategy's purpose became clear as he eventually had his way with her while the other 3 looked on from a distance. He's a very distinctive sort of squirrel, methinks.

And on the topic of calibrating my lens: I did buy the Tap-In Console for Canon(TAP-01E) as well. $44 used from KEH at the same time as the lens. The lens appears to function well with either the T6s or the R, so I'm assuming the latest firmware is installed and the Tap-In needn't be used at this point. I also understand that one can make all sorts of adjustments, fine-tuning functions to suit oneself, but that's a sure way for me to get a nice piece of gear royally messed up.

Maybe one day I'll play with the thing. Of course, none of my other current Tamrons are Tap-In compatible, the A005 70-300, the A09E 28-75, and the B008 Di II 18-270.

Your distinctive male is obviously the alpha male in your neighborhood & as such, he gets his way first w/all things including love making, food, deference, etc. The running in line is the group of male squirrels & they run in pecking order, i.e. Alpha, Beta, etc. Also, it may or not be of interest but male squirrels' testes only descend during the active mating period; otherwise they remain safely retracted & invisible until needed. Don't know your location & it depends on the sub species of squirrel, but for most, now is the peak mating season. I have found squirrels to be very entertaining and instructive to study & observe. Thank you for the lovely photos!