For some time it has been reported that tiff files out of Topaz will not successfully transfer back to Lightroom.
In my experience this is also true of Affinity Photo. Recently, some jpg files from Topaz have also been displaying the same reluctance to open in Lightroom where they hadn’t used to.
I have found that closing Lightroom (ignore metadata warnings and skip catalogue backup) then immediately reopening it forces Lightroom to accept these files. It’s weird but it seems to work.
I’d be interested to know if this works for anyone else who is having difficulty.