0.7.1: Linux - gradually growing lag (roaming, battles, etc)

Last post on the lag for now. Probably a general issue with something to do with the Linux port.
After playing the Linux version for a couple realms (mixed in a few save and restarts in habit), navigating realms is getting slower and slower (slow tile-tile speed with 2x movement).

Large amounts of treasure take awhile to display (yellow text).

So, it may be simpler than I thought.
The LInux version only gets 1 CPU core. (25% with 4 cores) While the Windows version uses 2 cores (50% CPU with 4 cores)

Steam Proton and native linux cpu comparison (992MB is native linux version)

Native windows (~50% CPU)