Recently I had experienced a lot of frustration with st 3 crashing in both Sonar and Studio One 4. And about 30 minutes ago I checked my st version it was 3.7.2. I went to ik website and found 3.7.3 to the latest version released in April 2018. Have been testing the latest version for a few minutes and so far so good. Err , no it just crashed. How are your experience with 3.7.3?

The VST3 version has never been stable for me.  The VST2 version is reasonably stable.  I generally recommend removing the VST3 version and only using the VST2 version of the IK instruments (Amplitude's VST3 seems fine, T-Racks I've had mixed results).  Not everyone has problems and there will be people claiming everything is good with the VST3 version, but that doesn't mean everything is great for everyone.
 
In either version there is at least one instrument that I know of that has a crashing bug (one of the Steel Pan instruments) that can be reproduced with the correct MIDI (simple) sequence (has some problems with G#4 or G#3 notes, I can't remember which).  IK knows about it and have used the files I sent to reproduce it but haven't bothered to fix it (almost a year now). 
 
If there is a instrument based crashing bug for at least one instrument then logic says there are crashing bugs in more than one instrument.  My test MIDI file crashes 3.7.3 just like every version of Sampletank before it.  Doesn't matter what DAW you use/etc.  The fact they admit the bug exists and is reproducible and haven't bothered to fix it bothers me no end.

I haven't had any problems with any version in SO V3 or V4.  I'm not a heavy user of it, but I do use it often.
 
When IK first started providing VST3 versions I had problems so I stuck with VST2 for a long time.  Been using VST3 for quite a while now without problems.
 
 

One thing that may be a factor in Samepletank3 crashes is it seems to be very sensitive to low latency settings.  As a rule I have to run a much higher buffer size with it than I'd like.  If you are running very low settings you may be seeing problems because of it.  My old Focusrite was never a latency king so I kind of expect it but for me Sampletank3 would run at reasonable latency, but if you dropped the number a little more it would start to crackle and pop and if you kept dropping it would hit a point where it would just crash.