The % is stalled at 0 [since the last upgrade or other conditions]
Check that you didn’t accidentally select GB (GigaBytes) instead of MB (MegaBytes) for the Quota in the Settings.. page (for example a quota of 500 MB would make sense but not 500 GB). Since 1 GB = 1024 MB, that would explain that the percentage looks like it is stalled at 0.