We've noticed that when running the game using FXAA for anti-aliasing, the highlights when holding alt were all offset. Decreasing the resolution appeared to decrease the offsets, but not fix it. Changing the windowing modes (exclusive fullscreen, windowed fullscreen, windowed) seemed to have any effect. It's like the camera plane and the overlay plane are offset, and somehow clipping through each-other. Zooming in and out caused elements to appear and disappear, even just part way (shown in the screenshot below).
Changing from FXAA to TAA fixed the issue. In addition, when switching back to FXAA after enabling TAA, the issue resolved itself until the game was restarted.
Unfortunately I changed a lot of things before encountering this issue, so it's hard to narrow down exactly why I'm seeing them now. I recently upgraded from a nvidia 2080s to a 3080 ti, as well as upgraded to the latest Nvidia graphics drivers (516.59 released on 06/29/2022). I was able to verify the same issue using my roommate's PC as well, with the same exact hardware and driver.
There may be some relevant patch notes from the Unity postprocessing package. I'm not sure which version is being used by Solasta: