Having the same issue too now for a few weeks. Updated chrome and firefox, cleared all cache and cookies. STill just really unpredictable and sporadic whether the admin panel will load or not. If it does it takes soooo long.
The only error(s) I’ve seen (and they don’t show up very often, mostly just a blank screen with light grey boxes where content should be) have been a 500 error and on stating ‘A technical issue prevented the page being loaded’.
Definitely no issues with the internet connection (fibre) as all other sites are working perfectly, as was Shopify up until about 10 days ago.