I think it was the 5.7.8 (Windows) release that introduced a bug that caused Arq to believe a budget of 0 should be enforced. This meant if you backed up to AWS (probably others too) it would delete ALL backup records except the most recent one (and then immediately cleanup the now unreferenced objects, so even the reflog feature can't help you)
I had only been using Arq for a few months so I didn't lose anything major, but if I had been keeping years of historical records, I would be furious.
This was fixed in the next release 5.7.13 ("Fixed an issue that could cause Arq to enforce a budget when no budget was configured.") but still - I thought a bigger deal should have been made of this.