Possible solutions to correct this issue.

Rebuilding the Default_Fix.ini file

Export iFIX process database to .csv or .gdb file format.
Find projectname_Fix.ini/Default_Fix.ini (C:\ProgramData\GE Digital\Industrial Gateway OPC Server\V7 ) and delete this file. iFIX does not need to be shut down when doing this.
Note: This folder is hidden and will need to be viewable by allowing hidden items in your file explorer.
Reload the Empty database or use the existing Process Database overwriting existing tags.
Re-import .csv/.gdb file export of the database. Importing the tags should recreate the projectname_Fix.ini/Default_Fix.ini.

Also, IGS 7.610a is currently out and it resolved some issues with crashing that customers were experiencing.
Link here for IGS 7.610a software : https://automatech.box.com/v/IGS
Please install and then test.

Lastly, please put the device into Simulated mode inside of IGS and start up iFIX. This will determine if there is an issue with your data server and the IGS.