mod_fcgid: error reading data from FastCGI server

I’m trying to debug a ‘mod_fcgid: error reading data from FastCGI server’ error as per https://www.virtualmin.com/node/40089

This is on a site where I have set up a Virtualmin virtual server as a sub-server. The idea here was that, although the two sites did very different things, it would benefit from all the backup etc stuff I had set up for the main server page.

Intermittently the server returns an Internal Server Error 500 and ‘mod_fcgid: error reading data from FastCGI server’ appears in the logs.

Whenever I try to set the main server to use a CGI wrapper instead it just ignores me and still uses FCGId.

I wiped the sub-server and the problem still occurs, just even more intermittently. I have tried Validation and Limits -> Fix Permissions and this made no difference. I suspect it is a memory or resource issue but want to see if I can track it down.

Any thoughts on getting the shift to using CGI wrapper to stick?