[Snapshot Pro] Cannot restore managed backup

I'm trying to restore a managed backup in a site but it stops at 40% and is failing with the error "Restoration Failed". We have tried increasing PHP's memory_limit to 1024M and max_execution_time to 300. We also increased corresponding WP_MEMORY_LIMIT values.

The following message shows up in the Snapshot log: "[snapshot][2018-07-06 22:52:43][Warning] Unable to extract manifest."

I also tried re-installing Snapshot which didn't help. Debugging was turned on but no debug.log file was generated. No errors were found in the browser console.

Please advice.