Thanks for your reply. Yes, the problem was with the stock message app. Popped in store a week or two ago and they seemed to know there is issues and advised to look out for future updates. I've tried rebooting, clearing data and cache but still kept crashing.
I've gone with a 3rd party app and having no trouble now... Textra.
You're very welcome @Mujj
I'm using the stock Samsung Messaging App on my Note 9 with Samsung One Ui / Pie and it's fine
A good way to tell if this is being caused by another app is to put the phone in Safe Mode which disables your downloaded apps and leaves the stock ones working.
If the Samsung Messaging App then works it's a downloaded app causing this issue.
Anyway I'm glad to hear a 3rd party app is working ok for you in the interim.
Current Phone > Samsung Z Fold³ 5G.
Just out of curiosity I tried the phone in safe mode to see. Same problem with the stock message app but good to rule out a 3rd party app problem.