Macros slowed down after Big Sur Install

So, I installed Big Sur (11.3.1) on my MBA, which is running Keyboard Maestro 9.2 and has been running KM for 7 years with no problems and now after one use of a macro, it slows down, from a few seconds to 30+ seconds. Quit the engine and relaunch and it works fine first macro and then slows down again and gradually gets slower with more use.

I've tried actions suggested in other slow down topic, including a reinstall and nothing has helped.

All the macros run fine on my iMac Retina 5K, also upgraded to Big Sur. The macros are synced via DropBox and have never been a problem.

MBA spec: 1.7 Ghz Dual-Core Intel Core i7, 8Gb mem

-- David

tried resetting (checking/unchecking) KM permissions in System settings?

Yes, assuming I’ve found everywhere it is listed.
— David

So thought I would compare the two macs Sys Prefs, not sure if this makes a difference, but on iMac, Security & Privacy->Automation, Keyboard Maestro is listed with KeyQue, System Events & Safari, but on the MBA it's Keyboard Maestro Engine with just KeyCue & Safari.

Is there a definitive list of settings it should have (allowing for the fact that owe all have different apps)?
-- David

UPDATE: noticed KME has used 2.3% CPU and KM 4% whereas on the iMac (used much more), it's 0.1% ea

UPDATE 2: so 1 hr later, without me using it, the engine is now at 17.1% CPU and I find 4 unfinished macros.Cleared those, tried again and first execution was normal, but it left a macro still running and second execution did the same, meaning there are now to running, isn't happening on the iMac.
And it appears to just be a group of macros - so one is giving problems - time for some searching.

Found it - user error of sorts! It's a series of macros and one replaces the current URL with a new one and then waits for Safari to finish loading the page for AT LEAST 3 seconds - appears Safari doesn't complete loading the page on the smaller screen!
-- David