IKEv2 VPN on macOS Sierra disconnects after eight minutes
The essence of the solution described there is plausible – that it has to do with the re-keying process which occurs periodically.  You ought to see something in the Console log, and perhaps also in logs on the server side, that will point you in the right direction.

At random times during the lifetime of the tunnel, the two sides will re-negotiate the symmetric-cipher keys that they are using, so that the conversation does not continue to use the same keys for too long.  If this process failed, the connection would be dropped, and if it consistently occurs "after eight minutes," this could well be it.  All of the parameters on both sides must match exactly, and there's nothing easy about debugging IPSec.  I'd start with Console as my starting point.  (There are several logs – look at 'em all.)