Time Machine backup issues with NAS and external drive

Replaced Time Capsule with NAS BeeStation Plus several days ago. Using Time Machine, the first backup took 24 hours and it hasn't backed up since then (for 2 days) despite being set to auto.

I believe I've set up the BeeStation correctly. I can see it on my MacBook Pro running Tahoe 26.2 and I can see files on there. Storage on MBP is currently at 600 GB (of 995 total).

Meanwhile I also have an external hanging off my MBP that I back up to alternatively. That too is taking hours (it's usually minutes) to back up.

I've tried the usual restarting, restarting in recovery mode and trying First Aid. All's well according to them.

Could Time Machine be the problem? Since I have the latest system, how would I replace TM?