If both a polkadot and moonbeam account are connected the wallet will not connect properly and just enters an endless loop of blank screens and requests to connect a wallet.
Have replicated this on both Opera and Brave with v1.7 and prior.
This is now fixed as of 1.9.0, ETH accounts are no longer a default option to be injected into a substrate dapp and vica versa
noted this can happen, esp with singular. We're updating the UI to make it harder to inject EVM accounts into substrate dapps