Comment by scottlamb

> Lately (last year or so) I've started to notice substantial data loss. Either old mails completely missing or large mails being truncated (destroying inline images f.ex.)

Please write to support and ask them to investigate. I used to work on the Gmail backend team, so I know bug reports regularly make it through support to an engineer. I also know they take data integrity quite seriously and have a variety of tools to investigate (potential) problems, both proactively and in response to user complaints such as yours. They also keep redundant copies of everything.