Version 1.21.1
When I use Open Parties and Claims and force-load the chunk the pumpjack is in - it doesn't work, tanks and pumps still work.
I also use Does Potato Tick, but have mods whitelisted and server core.

It's possible that pumpjacks use random ticks so they are unaffected by forceloading.

Works just fine for me, at least with the /forceload command. It does not use random ticks