An x nozzle is a hardened steel nozzle made from vanadium carbides. It is very hard and resists wear. With brass nozzles and my typical printing amount (800gm a week +) I was replacing nozzles almost every week. More abrasive (filled materials, carbon, and glow) more often. When a material would string with settings that normally work well, or you get blobs and such, I pulled the nozzle. The X nozzle has run 6 KG and is still perfect as near as I can tell. It needs to out last at least 10 brand name nozzles to be worth it. So far so good.
One of my printers would start under extruding in around that range, it sometimes would stop completely 30 layers later. On occasion loosely 50 layers after that it would start again.In mid air…
I traced it to an over heated stepper. I hope that isn’t your issue but it is a remote possibility. The micro swiss doesn’t use reduction gearing like the E3D DDs typically do. It puts and heavier load on the stepper. Extruder steppers and generally smaller and lighter (too keep the weight down) they could be more prone to overheating. This can manifest in missed steppes where it stops turning and you get little gaps, then more gaps then nothing.
Something to keep an eye on.