I’m not able to recreate the situation but I found myself on a server with just one other person (after 1-2 minutes) we both start on the defending side of Train Yard.
The other player swapped teams and started playing Proxy. When we for to the 2nd stage and had to blow the train carriage she placed a mine over the C4. However the mine would not detonate when I attacked it. Full clip of primary and a clip if secondary but nothing…
Didn’t think that much about it but then though it maybe related to the team swap etc so thought I’d report it here.