Bitcoin Core shows addresses that Electrum says don’t belong to my wallet (imported MPK via EPS). What is going on?

I got a full node (pruned) up and running with Bitcoin Core via Tor. I installed Electrum Personal Server (EPS) and connected my hardware wallet with Electrum via Tor. I generated a watch-only wallet in Bitcoin Core of my hardware wallet by providing the master public key in the config.ini file (no other master public keys, only the one of my hardware wallet as shown on Electrum). Everything works: I get the green circle in Electrum, saying I’m connected to (only) my own node, and I can watch my wallet in Bitcoin Core.

However, Bitcoin Core’s “receiving addresses” show addresses that do not belong to my wallet according to Electrum. I tried to send a test amount to one of the addresses in Bitcoin Core that were not shown in Electrum. This transaction now shows in Bitcoin Core as belonging to one of my watch-only addresses but does not show in Electrum. The ismine(“address”) command in Electrum returns false. I also can’t sign messages with the address in Electrum with my hardware wallet connected as Electrum says the address doesn’t belong to the wallet.

I double checked that only one MPK is mentioned in EPS’s config.ini file, and I also created a new wallet in Bitcoin Core and resynced the EPS. Same problem: my wallet now shows a different amount in Bitcoin Core (including the abovementioned address) than in Electrum (excluding that address). Bitcoin Core is showing many other addresses that are not present in Electrum, besides this one that I sent a test transaction to.

How is this possible? The Bitcoin Core wallet has private keys disabled + blank wallet and is named “electrumpersonalserver”, so it should be dedicated to EPS and since I only imported and master public key, shouldn’t it contain only addresses derived from that one master public key?

Is the issue that Bitcoin Core has derived an address from my master public key that Electrum hasn’t generated yet? But I’d think that Electrum should recognise all addresses that belong to the wallet (and ismine returned false and I can’t sign messages with the address in my Electrum wallet as it says the address doesn’t belong to the wallet). Or shouldn’t I have imported the master public key through the EPS config.ini file (and rather imported it through the Bitcoin Core console)?

I would be very grateful for any help and insights into what’s going on here. Many thanks in advance!