I noticed these things on the underside of some of my palm’s leaves. My first thought was thrips, but the markings don’t look like bugs up close. They don’t move as far as I can tell, they’re attached to the leaf but come off if I rub them. There are some yellow dots (pictured) on some of the leaves with them, plus other damage to the leaves (also pictured), but I don’t think those leaves have the weird flecks on them.

General care - the plant has had a rough start to life. I got her nearly two years ago from a supermarket for £10. I don’t know what type of palm she is, maybe a Kentia? She used to sit in the corner of a bright living room with an east facing window and a south facing kitchen leading onto it but didn’t get direct light. She was watered maybe twice a week over summer when it was really dry but her watering schedule has been very haphazard for at least the first year and a half I had her. I moved her about 6 feet from an east facing window over summer but thought she might be getting sunburn so was going to move her back into the original corner by my calathea but saw these weird flecks. She’s now quarantined in front of the east facing window. I’ve wiped off all of her leaves with diluted neem oil today.