Resolve 17.4.6 + macOS Mojave 10.14.6 = no thumbnails

Resolve 17.4.6 + macOS Mojave 10.14.6 = no thumbnails and no preview (Resolve 17.3 was OK)
Hello! For some reason i still use macOS Mojave 10.14.6 as my main work system. I know that formally Mojave is not supported starting from Resolve 17, but for my opinion everything worked fine until i decide update from Resolve 17.3.2 to 17.4.6 (I also tried install Resolve 18, but the installer don't allow me to install it on macOS 10.14.6 at all)

So here is the explanation of the problem with Resolve 17.4.6:
When i import old project(s) that use DNG, ProRes and BRAW and any other sources - all thumbnails as well as video preview in viewer is gone and i can't do anything with it. "Refresh Thumbnails" command didn't helped.
In addition when i close Resolve - icon in dock remains active for endless period of time, so i need force quit it. It looks like some sort of strange hang.

Here are few questions to developers or tech support:
1. Is this some sort of bug or something was changed in Resolve 17.4, so it can't handle old projects or legacy macOS anymore?
2. If this is a bug - any chance that we can see version 17.4.7 that will fix this problem?
3. Is it safe to use Resolve 17.3 macOS 10.14.6? Are there any technical limitations or warnings that i should know about this? Resolve updater pop-up window still promote me update to 17.4.6, so i guess it detects my system as compatible?

Another really strange thing here: if i create new project in Resolve 17.4.6 and import same footage there - thumbnails are visible and everything works well. Any ideas why it happens like this
I really need to use old projects somehow and same time i really would like to use Resolve 17.4.6.

And another really really strange thing here:
If i create new project, save it and then open legacy project - i can see thumbnails in legacy project.
If i open any already saved project from start (even project created earlier in Resolve 17.4.6) - no thumbnails.

Seems problem not only in my setup. I done a search for world "thumbnails" search.php?keywords=thumbnails&fid%5B0%5D=21 and it looks like there are a lot of other similar reports and threads about missing or glitching thumbnails as well as random "media offline" from macOS/Windows users. Reports where started after Resolve 17 release and the next large wave of reports was after 17.4 release.

In 17.4 i also noticed some changes in files structure in folder ~/Library/Application Support/Blackmagic Design/DaVinci Resolve/Resolve Disk Database/Resolve Projects
So i guess problem really caused by some changes in 17.4 and higher