I have Ver 9 installed with no tweaks of any kind, just my own apps and I am using magi 19.3 (19300 latest version)
I have none of the above reported issues, phone is performing perfect as it did on ver8
I did hold back on installing 9 after reading some issues about lags and crashes. I did dirty flash ver 7 and 8 and had no real issues except all share did not quite work. So I did a fresh clean install of 9 two weeks ago and I have had no issues since and all share works perfect now also. All apps and widgets perform as expected.
For those having lags or crashes it must be some addon or tweak that it being used that is causing a conflict, try a clean install with no tweaks and if that is all ok, then gradually add your tweaks one at a time and test for a few days and so on, until the lags or crashes reoccur, that way you can isolate the problem.