If the extension keeps on loading and does not show balances on all networks like this, try the following steps.
Step 2: Brave will ask you to relaunch the browser so that the change can take effect. Click Relaunch and open SubWallet extension again. Your balances should all show up now.
This might result from a broken link to the nodes. Follow these steps:
Step 1: Reload the network using the Reload icon next to the network's account. If the network continues to load, move on to step 2.
Step 2: Click on the Edit icon to edit the network endpoints. Under Provider URL, click on the drop-down menu and choose a different link. Hit Save, then hit Done.