It could that the snapshot was successfully created but the filesystem can't mount it. This could be resulting that the xfs is corrupted or not enough resources to mount it (memory).
You can try to run the "Repair filesystem on LV" from the Extended Tools function in CTRL + ALT + X.

If this does not fix the issue send logs from STATUS > HARDWARE > LOG then click on the "Download" button and send logs to support@open-e.com