Backups not completing

Backups aren’t completing — they work for a bit, and the blue bars both go to 100%, with the top one saying “Job completed” and the bottom one “Job done in 0 seconds” (even though it takes longer than that) but the log is locking up at “Compressing files as ZipArchive. Please be patient, this may take a moment.” (after “1. Trying to create backup archive …”) and all the files don’t get included in the resulting .zip.

I’ve tried a few different times, with similar results each time. This is on MediaTemple if that helps. Plugin version 3.6.10, WP 5.2.2..

Any guidance appreciated.

(This was a task for a client that should’ve taken 5 minutes tops, and now I’ve spent about 45 and have a manual download of all files in progress in FileZilla (NOT ideal).)

Thanks.