Problems restoring WhatsApp backup from Jolla to XA2
I've just recently upgraded from my trusty old original Jolla phone to the XA2. All went smoothly, Sailfish was booting on the XA2 without any trouble at all and I'm definitely enjoying the extra horsepower and nicer screen. However, my WhatsApp messages backup is not restoring for me. I created a backup file on my old Jolla, it's about 16MB. I transferred the backup to my PC via USB cable and MTP mode, then copied it to the same location on my XA2 in the same way (via MTP mode). When I installed WhatsApp, it didn't find the backup at all, instead starting straight after verification into the app, with my chat groups present but no messages. I tried renaming the backup file to the standard database file and reinstalling WhatsApp. This time it found a backup, but listed it as 0KB in size and dated 1970! Choosing to restore this backup didn't work - it failed after a couple of seconds of processing with a message saying sorry, we can't restore your messages.
Any questions I've already come across tend to suggest copying the entire android_storage directory. I did also try copying the entire WhatsApp directory from android_storage to the new phone, but it still came up with a backup of 0KB from 1970. After trying so many times (and reverting to my old phone to re-make the backup file), the WhatsApp verification step has blocked me for 13 hours, so I'm very limited in what I can try now. I sent a message to WhatsApp support, but immediately got a response telling me they don't support rooted devices and will not answer emails from me.
Is there anything I can do to get my messages over to my new phone? Is the 0KB and 1970 thing a clue towards some sort of issue?