I recently reinstalled WhatsApp because it stopped working. Then, I restored the Google Drive backup. For this backup, I used my primary Google account. Restoring worked fine.
However, after restoring the backup, no new backups would work. It always just got stuck at some percentage of progress. After many failed attempts of canceling the backup after hours of being stuck at the same percentage, I added my secondary Google account to my phone and chose it as WhatApp's backup location. It then went on to make a 2.3 GB backup to the secondary Google account (according to the information WhatsApp stated). This backup again got stuck. Repeating it several times always made it get stuck at a higher percentage of progress.
Eventually, I gave up and deleted the backup in Google drive (secondary account). I noticed that my secondary account only used a few hundred MB in total, according to the information found in the bottom left corner of the Google Drive website.
After deleting the backup, I started another backup. WhatsApp showed that it already completed 2.3 GB of 4.6 GB right from the beginning. This got stuck again at 99%. After deleting the backup again and starting it again, it now started at 4.6 GB of 6.9 GB, apparently always increasing by 2.3 GB.
What should I do to perform a full backup?