Blue Iris

Have an alert setup on motion to send web request (json line )

Very simple so ...

192.168.8.4/JSON?&request=runevent&group=GROUPNAME&name=EVENTNAME

90% causes BI 5 to just immediately quit.

Any help appreciated

In fact BI now is completely unstable and crashes regardless of alert.

In your shoes, I'd try to launch BI, and then import a previous REG file that worked. Page 215 of the help file describes the backups.