This was not only happening on Firestorm viewer 6.6.17, BUT also isues on SL viewer. Touching any group to change, or trying to use landmarks on notecards: All December, both myself and my wife (on separate pc's) were having the same issues. Any time we would go to use a landmark on a notecard, (whether I made the notecard, or it was also happening with the Hop Around Event notecard) or touch a group to change during advent, we would both bugsplat. Once a bugsplat occurred, we could not log back in for hours and sometimes not until the next day. We would both try the sl viewer, and could not log in there, same goes with the mobile viewer, so it was obviously an sl side issue otherwise why could we not log in on any viewer? When I could not login because of the bugsplat, my wife tried to log me in on her pc and she could not accomplish it there. I also tried her account on my pc when she was unable to login, same result on my pc. It was NOT an internet issue as she was still online when I was unable to login, and vice versa. Rocky Linden in support tried to help. Neither he nor Freckle Linden could find anything wrong with my account or my inventory. Rocky closed my support ticket and suggested I write everything here. The support Ticket was #2446401, you can find all the times I was bugsplatting listed there and the attempts to rectify the issues. During all this, I tried changing to a system avatar, no fix. I uninstalled viewers, reinstalled them, no fix. I cleared all caches, no fix. I have had many more problems than these ever since I started this account. I really think part of it may be the server my account is in as my wife has not had many troubles at all in comparison. The last bugsplat I had was on New years eve. I have been afraid to change groups or use landmarks since. I found an interesting notice on the sl viewer. It states that login and intermediate inventory issues were resolved on Dec 6th. That is right around the same time we both began having this recurring problem with group activations and landmark bugsplatting issues.
Below are 2 gyazo pictures of the error messages I was receiving on sl viewer when I could not log back in as well as the dec 6th message for reference.