Anyone else seeing tremendous WISP slowdowns on UBNT 5.5.10 (versus 5.5.6)?

We have a neighborhood setup in the Santa Cruz mountains, where we have
been debugging a radio slowdown problem for weeks.

We replaced the router, the cables, the radio, etc., and just today,
we figured out, almost by accident, that simply updating the Ubiquiti
firmware from 5.5.10 to 5.6.2 (which we did a while ago), was what
seems to have caused the appreciable bandwidth slowdown.

Has anyone else out there seen a huge slowdown in speeds when you
"updated" your Ubuquiti firmware from 5.5.10 to 5.6.2?

Any idea why?