On May 14th our channel with LNBIG-42 was force closed and has only returned to the wallet minus some fees a few days ago.
From what others are telling me it was most likely due to an expired HTLC which likely caused the automatic force closure as per the default settings in the relevant lightning implementation.
HTLC relay failure leading to node downtime seems to be the cause, but it is hard to say what specifically about your node setup and channels may have been vulnerable to this situation.
Also mentioned, it is possible the remote channel was misbehaving in some way. This is why until you can be certain that you are avoiding all related vulnerabilities you should not open channels with lots of unknown people especially not with questionable reputation.
Can you please tell me if I can raise the default HTLC settings on my node to hopefully avoid this happening again? Maybe using RTL or Thunderhub? Since it was not our side of the channel that initiated the force close why did we get charged fees?
Thank you for any assistance you are able to offer.