I've been getting a few raids that end up as a win for the bugs raiding, after 2 rounds of bugs appearing at my base then on the 3rd round nothing appears and then I get the "Payback delivered..." message. Am I doing something wrong or is this a bug?

It's not really a bug, it's just a nuance of the game. Beetles on the way to the base can get stuck somewhere, stumble upon free-standing buildings (and start destroying them), etc. As a result, after some time, without seeing them at the base, we can either receive a corresponding message about the completion of the raid, or the raid may even hang. The last option is especially unpleasant. I already wrote in some post on this topic that it makes sense to add a time limit for the raid to the game.