DXO just released version 1.2.2 which corrects the plugin bug introduced with the latest Lightroom Classic CC.
Just downloaded and installed the new version, and now it works as it once did to send an original image from Lightroom to DXO and then reimport the edited TIFF back into Lightroom and stack it with the original.
There still seems to be the delay re-importing, but it might be down to 35 seconds from a consistent 40 seconds ;) The delay, while a hassle, is OK once you know what is going on.
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