Tonight's OS update & upgrades (smoscore & stellarsolver I think) kill my system,
Kstars goes into a boot loop then removes itself along with PHD2.

I reflashed a fresh 1.5.5 image, and ran update & upgrade again and it does the same
anyone else running the Beta OS 1.5.5 and having issues.
The OS has been running great before tonight's update.

I Reflashed and tried to run update / upgrade again, and it does the same thing, after a reboot Kstars just runs in a boot loop till it deletes itself.
You can run autoremove to remove INDI/Kstars and reinstall, but it no longer shows up as a stellarmate device from the app, and webmanager doesn't work anymore either.
I'm using a RPi4 4gb with the latest eeprom update, maybe its that?
I'll reflash and won't run any updates for the time being.

I have another rpi4 4gb that I haven't upgraded the eprom on, I'll reflash with SMOS 1.5.5 and upgrade that and see how it runs?

You are not alone. I have same symptom as you Kstar boot loop. I restore to last backup before update and look for solution.