MR1100 - issues when not on default IP Address

So we've got a number of the MR1100 wifi 4G routers, and with all of them (pretty much without fail) when they are given an IP Address of anything other than the default (192.168.1.1) they regularly fail to perform to the same standard as when all networking settings are the default.

This includes having DNS issues, being unable to even get to the router admin page to login, being able to finally connect but then experiencing massive latency.

If I use the same device with everything reset to default, bingo!! No issues whatsoever.

Any ideas as to what could be causing this to happen?  I'm losing the will to live, and do not want to reconfigure our other networks IP ranges just to accomodate this pos hardware