Having not known what gather mate was I looked it up.

Apparently it's a legit mod that tracks the locations you've gathered from. Ok, so my thoughts on this is that this inadvertently got you banned.

When I gather I don't use mods that highlight my herb locations. So for example if I farm in zones I am just usually wandering around aimlessly on a loose circuit looking for herbs to gather. But if I had this addon I'd be more likely following a very specific pattern knowing where they spawn.

Ok so having said all that what the GM probably witnessed was your characters repeating a specific set of locations over and over again. Very bot-like behavior.

If this is the case then your accounts got mixed up with what bots typically do. Multiboxers already get tons of reports thrown at us because players hate what we do. Normally it's a non-issue but this can look like a bot and that may have been enough to get your 6 month suspension. As someone else said above this all assumes you are being honest with us.