Expressimo RB 250 mistracking issue

I have a mistracking issue with my Expressimo RB250 / Shelter 501 MK II combo.

I was away for 6 months and wasn't listening to my vinyl rig, now when I got back I noticed that my cartridge started to mistrack a couple of LPs I own.

Those LPs are Direct to Disk editions that have a few very dynamic passages recorded but the cartridge was tracking them fine before. Now it mistracks them (you can clearly hear it on a drums solo when a drummer hits snare drum). Also on a Hi-Fi News Test LP I can only successfully track tracks 6 and 7, but not 8 although I was able to tack #8 before.

So what could've go wrong? I tied to adjust anti-skating, but I increased it all the way to the top limit and it still mistracks. I remember before I had anti-skating set at around 1.4 - 1.5 on the scale from 0 to 2, now even if I move it all the way to 2 it still mistracks.

I'd highly appreciate if anyone could help/recommend what can be done to fix this? Is it a tonearm settings or cartridge problem or something else?

Thank you in advance.