So I've been putting together a multi-month long timelapse. I import the photos into Lightroom into albums that represent one month at a time, each album containing ~13k photos. Originally, I had no issues copy/pasting my edits to an album, but something happened ~2 weeks ago and now it's horribly slow. For context, I'm running on an Apple MacBook Pro M1 Max, 32GB ram, etc. In Settings -> Performance, "Full Graphics Acceleration is Enabled".
Initially I discovered that Adobe had uploaded all my albums and had apparently therefore removed many of the files locally. Therefore, when doing the edits it had to redownload each file as well, so I set each album to "Store Album Locally". It went through an extensive re-syncing process, but once it finished, it's still just as slow as before. The pasted settings only get applied to ~1 photo per second.
My MacBook has ample resources available to it, as I've confirmed Lightroom is only using ~100-150% of resources when pasting edits, so a little more than one CPU core, and it doesn't seem to even be touching the GPU. As opposed to when I do an export of one of the albums, it jumps to ~900% utilization as Lightroom cranks out the files as fast as it can. Memory isn't even close to being an issue.