The only one I found was 'Turn on MIUI Optimization'. But turning that off made it worse if anything.It looks like some newer versions of MIUI ship with a feature called 'memory optimization' hidden in developer settings which also auto-kills background apps; go into developer settings and disable that feature and that should hopefully fix this
There is also the issue of the Notification turning into a floating button. That appears to (a) only happen with OCR, not screen reader, and also (b) seems to only happen once. But of course with the service turning off regularly, once becomes a lot more often!
I can understand that the service stopping could be system-dependent, but is the notification switching to button?