ProTools 12.8 changed the way Soundminer can auto-detect the running session. If Soundminer isn’t identifying your session changing, try the following.

In ~/Library/Preferences delete the Avid folder… The user Library folder is hidden by default, so you can hold the alt/option key down and in the Finder, use the Go menu and “Library” should show up.

Go to macOS Security Privacy Settings -> Privacy-> Full Disk Access. Make sure Soundminer is checked in there. Also take a look at the Automation pane and Accessibility sections.

You can also try this info, as provided by Avid. In ProTools…
Setup > Preferences > Operation > Misc > now contains “Local Waveform Cache Versions” in PT HD (not PTSW). A value of 0 is the default which prevents any local wavecache files to be stored locally for use with NAS. Any other number up to the max of 99 will allow that many waveform cache files to be copied from the network drive to /Users/Documents/Pro Tools/Local Waveform Cache. Once that number is exceeded, the oldest waveform cache will be deleted. Oldest is defined here as the waveform cache that has not been used for the longest period of time. The default setting of zero for this preference represents the legacy behavior, which is required by Soundminer.