occasional blobs with PETG and even PLA  

RE:

Are you using a HF nozzle?  I never had issues with PETG doing this until I swapped to the HF 0.4 nozzle.  Swapped back to the regular 0.4, and problem disappeared (same filament, same models).  I think the HF profiles need some sort of adjustment for the nozzle's characteristics that Prusa hasn't completed yet.

Aside from that...  This problem can also be caused by wet filament (especially with PETG) or over-extrusion.  If you have dried the filament, you might try reducing the flow rate slightly when slicing.

Also, infills that overlap (like the default Grid) can cause buildup on the nozzle and eventually deposit a "blob", so I generally use Gyroid now. But your photos show it occurring before infill, so that isn't the issue here -- but something to keep in mind if you see the problem only when doing infill.

RE: occasional blobs with PETG and even PLA

Thanks, @ScottW.

Yes, from what I understand MK4S kit comes with a high-flow nozzle. I will keep an eye on updated profiles.

The filament is relatively new and was recently dried and stored in a box with humidity monitoring; so I do not think this is the problem. This usually doesn't happen during infills and with infills it's less severe since the blob can fall inside the print.

I'll try to perform a flow rate calibration.