Been awhile since updating that far back. We inherited a dozen devices - 750s and 912s. Wasn't there a warning about updating to far forward? As though we needed to step up to 6.33 before attempting later like the stable version now?
Thanks
If these devices have the Winbox port exposed to the internet, then I would assume they are compromised. I would make the trip to netinstall them along with evaluating the networks behind them to see if they are compromised as well. See https://nvd.nist.gov/vuln/detail/CVE-2018-14847 regarding RouterOS versions older than 6.42 that had the Winbox port publicly accessible. When this was published, attackers scanned the internet searching for vulnerable routers and found many.That's very old, lots of security holes, metinstall is your friend