I have a 2015 Shield. Best device I've ever had, and haven't ever had to factory reset it.
My main recommendation - in case it applies to you - is to not run any server software on it (eg. Plex). It's a solid client device, but has never had what it takes to run server services.
I think it has plenty of life left in it, so a factory reset might be worthwhile. Also note that the drive in yours may be well past its best.
Sophos. During their "edge protection is ALL the malware security you need or should have [and just happens to be what we sell now]" phase ~20 years ago.
Had a stand-up argument with one of their clowns when I worked as a security consultant. Ensured I would never do business with them. The guy was a mindless cultist before it became popular.