I know there is already a thread about this happening to someone else, but I quickly scanned the last 6 pages of comments and it appears to have devolved into a discussion on customer service and whatnot, so I decided to start a new discussion.
I just opened the app and noticed my characters were slightly off from where I know they normally are and sure enough, my 5* Strange is missing. I am 99% sure it was there yesterday (as I did not notice the shift in character placement). I am 99.99% sure I did not sell him or have him sold in any other accidental/bizarre fashion. Were it not for @d90 's post, I might have even just shrugged and said screw it (I’m a fairly casual player, my 5trange was only 1/1/1 and I never used him so not the end of the world), but this seems too coincidental.
I can answer question 2 at least. In the upper left corner of the app there is a gear symbol that opens the Options menu. Go there and then press the Help button. In the top right corner of the new window is a speech bubble Icon. Press that and start typing your request.
CS tends to prefer to be contacted this way i my experience as it also includes technical data about the device you use, so it helps speed things along in their end.
Out of curiosity, this wasn’t on the 3* node for Deadpool Daily today was it? 3* Strange is required, so 5* Strange is locked out and moved to the end of your roster when selecting characters for that node.