It must be a problem with Electrum communicating with Trezor to know that it has the private keys available to sign those UTXOs? Not sure how those two talk to each other to get that information across if thats even how it works
It's not. Trezor (any hardware wallet) only shares the xpub (master public key) with Electrum. No private keys are ever shared, that's the point of using a hardware wallet.
When you say EPS do you mean Electrum Personal Server? I've never used Electrum Personal Server, so I can't comment on any configuration settings, but I would suspect that's the issue. If you allow your Electrum client to select a server automatically does is show the correct balance?