The save game file (the .d2s file) unfortunately uses a checksum. If it doesn’t match the rest of the file, the game won’t load it and you get the “Failed to join game” error. So one thing you can try is to force a new checksum by changing the file.
Go to https://dschu012.github.io/d2s/ and load the problematic d2s file. Then click the arrow beside “Header” and add a letter to the end of the name, then go down to the bottom of the page and click on “Save D2R”. This should force a recalculation of the checksum and may allow the file to work again. Maybe. Hopefully.