Are whitespaces a good idea for a rootCA or intermediateCA for a self sign/closed on-prem PKI - with iPads?
Most probably you have installed the intermediate certificate in the wrong place. The root certificate should be added to the trust store on the iPad - this you've got working already.

The intermediate should NOT be placed in the trust store - instead it needs to be installed in the Keychain instead.

Spaces in the file names haven't got anything to do with the problem, as the file names "disappear" when the certificates are imported.

Note: In terms of "best practice" the way you are preceeding are more or less a work-around for the fact that you've got a misconfigured server/F5. You need to install the intermediate certificate on the server/F5 (i.e. whatever terminates your SSL), so that the TLS server actually replies with the full chain including the intermediate certificate.