I'm not quite sure as to why it's happening, but starting the campaign seem to double max speed bonuses, I suspect but cannot confirm that other maneuvering stat modifiers are being applied twice also (see image below)
https://prnt.sc/sFDjGKnXfLMpThe wolf, with a stock max speed of 150, is being modified to (150+250+250) = 650. If you use instead the refit screen in the missions, we see the image below with max speed bonuses being applied once
https://prnt.sc/7M3rq6bkyyvp
Strangely, if you boot up campaign, exit campaign, then use the mission refit screen, you also get the double max speed bonus. I suspect something is triggering that script during campaign start.
edit: ModPlugin seems to call adjustSpeedAndManeuverability on application load and on game load -- I'll try disabling one and see if it fixes the issue
https://prnt.sc/fMMG6nAHYAP_edit2: doesn't seem to have done it. On a side note, if you boot up a campaign, exit said campaign, and then boot up another campaign, max speed modifiers apply
three times