I don't think its a bug or caused by a mod. I've had that before, Ten Pines sending me someplace other than Corvega, and yeah, it was Walden Pond to clear out the raiders there. It's a rare occurrence but it happens, I've read of it happening to others before too, so..., don't really know why it happens.

It's actually possible in the vanilla game, but only very rarely, since you need to have already cleared out Corvega, and possibly even more Raider hideouts before you'd get to Walden.

Basically the quest is the same as any other Minutemen radiant, but it's not completely randomized. But if you already have Tenpines it changes settlements, and presumably if you've cleared out Corvega it changes Raider dens.

Yeah, I can see all of that causing changes in the quest location. For me it happened in a playthrough sometime late last year so I honestly can't remember the situation. In other words I have no idea what I had been doing or where I had gone prior to the TP quest. I just remember that I was so used to going to Corvega from TP that I went there, cleared it and when the quest didn't complete I looked at the details and found they wanted me to go to WP and I was like, WTF? That's the only thing that makes it memorable to me.

You always get sent to a settlement close to Sanctuary (usually Tenpines Bluff) and a location nearby said settlement (usually Corvega) but it can differ.