you have to put 3 level 3 mechs in your team

i did that and it still wouldn't count it

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You have to play the 3 tier 3 mechs in the battle spawn in all 3 and try to get a kill with each one just having them on your team and not using them won't work, I had this issue with the tier 2 mechs, if it doesn't work then I guess it is a bug

That may be the case but it's not what the objective says or how any other similar objectives work. The whole gearhub quest system is broken. Just another big update fail...

The Gear Hub itself performs all alright, but the Tasks are still being optimized. However the predominant majority of them are already fixed!

It's basically the same system with almost everything still behind a pay wall (anything I don't have, which is a lot of items, takes me to the shop to purchase), increased acoin prices for previous items in the progress path, having to purchase worthless junk to get to the good stuff (which then makes the wanted item even more expensive), nothing worthwhile can be obtained with credits, even worse matchmaking now since tiers are inter-mingled in pairing very weak opponents against strong ones, etc. It's all just a flashy re-design of the same old system. That's why it's a big fail. Just another way to push predatory sales...

And no, the majority are not fixed. Only a single task corrected itself so far, out of nearly 15 or so that are still bugged. The achievements for mechs still haven't been fixed either which is going on months now so I don't expect anything to be fixed for a long, long time or if ever...