I sent an additional support message today after the Nik 5.2 release…
Nik Collection 5.2 does not fix the problem.
It can still take upwards of 2 minutes for Lightroom Classic to be usable with a TIFF edited using Silver Efex via the “Edit In” menu option at the top of the Lightroom Classic screen. This has been a problem in Nik Collection 4.x and 5.x.
Other 3rd party apps such as Topaz Labs AI apps produce TIFF files that are instantly editable using the same “Edit In” Lightroom Classic feature.
I really think this problem needs to be escalated to your engineers. It is 100% reproducible for me and other people on your forum. If they can reproduce the problem then they can fix it. The problem is likely something to do with your TIFF file format causing issues with Lightroom Classic. Other companies produce TIFF files that don’t have these problems.