Bouncing between top 4 and >100 for month+?

We rank for a small set of keywords on a topic in the top 5 (2-4 usually), but only around half the time. We are #2, then >100, then in a few days back to #3, then a few days of >100, then again at #2...

At first I thought it would be very temporary, but this on/off result has now happened a dozen plus times over what is now a month plus. I also thought it was a tool error, but I've been able to confirm the on/off results in Google searches. SEMRush appears to be correct both about when we are top 4 and not in the top 100.

Has anyone else experienced this? There are no complaints from Google Search Console or anything else that indicates a on/off issue with the website, and this doesn't occur except for this keyword set currently.