A page that could not load says so, and that your store was not changed, with Try again and Back to Home. Press Try again first.
The grid kept its rows, with a yellow message
A reload after a save failed. The rows are still there, your draft is saved, and Try again reloads.
"We could not tell whether …"
An action whose answer was lost, a save of fields, Apply, Discard, Remove, an export, an upload, keeps the page and says "We could not tell whether applying started" (or whichever it was). The page then reads once to find out. If it did start, the page moves on; if not, press again.
"These changes are not here"
A result page whose address is for a change the store does not have. It was deleted with the store's data, or the address is wrong. Back to Home links the latest change.
"Open metangelo from your Shopify admin."
The app's address was opened outside Shopify. Open it from your admin, under Apps.
Still stuck
Write to support from the help centre, with the name of the page and what you pressed. Your draft changes are kept; nothing is lost by closing the tab.