Based on what @dnmr described:
When moving spidertron as driver to the center of the base, FPS/UPS decreases to 20.dnmr wrote: ↑Fri Aug 28, 2020 7:08 amwe've had similar spidertron related performance issues before https://www.reddit.com/r/factorio/comme ... _clearing/
If I ran to the center of the base with my feet, then the UPS value remained the same - 60!
How to repeat:
1) Load save game.
2) Sit in the spidertron and move to the approximate center of the base, near the storage boxes.
3) Get 20 UPS on the monitor screen
Saving the game at this point with 20 UPS on the monitor - attached.