First layer "tidal" waves  

First layer "tidal" waves

I'm having occasional problems with my first layer, particularly with the Azure Blue PLA from Prusament:

The transparent parts are correct (measured with a micrometer), but the darker spots are FAR too thick.  In this case, I printed without issue a few pieces (both different from this and prototypes for this).  I changed nothing, let it cool down before printing, and it has continued to print this way.  I redid first layer calibration in case that was off, and it didn't help - I had it happen during a calibration.

Prusa Mini+, first layer settings are PrusaSlic3r default, changing to a different filament usually fixes it.  First layer calibration is confirmed with a micrometer.  Only non-aesthetic change is a bondtech heat sink.

My best guess was the extruder was too tight, compressing the filament and causing inconsistant extrusion, but when it stopped working (after it had worked fine for a couple prints) I loosened it about a full turn and it didn't fix it.  I can't imagine that it would have printed fine the print before then does this based on overextrusion if loosening a full turn didn't solve it.

Has anyone else had this issue?  I can't seem to find it anywhere (if I search for first layer waves, its usually tiny waves due to slightly-too-close first layer).  Any ideas what it could be?