I'm having almost the same problem but sometimes I can play for 30 minutes or so on multiplayer. Getting the same error message at the end of arma3.rpt:
ErrorMessage: DX11 error : buffer Map failed : DXGI_ERROR_DEVICE_REMOVED

http://feedback.arma3.com/view.php?id=2531

Yes, I was trying to play Escape from Stratis and it's crashing with the same error.

With -winxp I had no crashes playing singleplayer, finished all showcase missions. In multiplayer I'm mostly playing Wasteland and getting the same error message in arma3.rpt as I had in singleplayer without -winxp.

This is the error:

DX11 error : buffer Map failed : DXGI_ERROR_DEVICE_REMOVED
DX11 - device removed - reason: DXGI_ERROR_DEVICE_RESET
DX11 error : buffer Map failed : DXGI_ERROR_DEVICE_REMOVED
DX11 - device removed - reason: DXGI_ERROR_DEVICE_RESET
Virtual memory total 4095 MB (4294836224 B)
Virtual memory free 2616 MB (2743988224 B)
Physical memory free 5744 MB (6023634944 B)
Page file free 5040 MB (5285089280 B)
Process working set 946 MB (992731136 B)
Process page file used 989 MB (1037340672 B)
Longest free VM region: 2145656832 B
VM busy 1549086720 B (reserved 367169536 B, committed 1181917184 B, mapped 85651456 B), free 2745749504 B
Small mapped regions: 21, size 102400 B
VID: dedicated: 913702912, shared 3354996736, system: 0, max: 730962340, used: 666312704
ErrorMessage: DX11 error : buffer Map failed : DXGI_ERROR_DEVICE_REMOVED

Happened again, even with the -winxp parameter. Exactly the same type of crash. I was playing online for about 40 minutes and the game crashed. I was also experiencing extreme slowdowns on random, game was freezing for 5 sec or so then continued working. I've uploaded a new archive with the files after the crash. Hope it helps.

After adding the -winxp parameter I'm able to finish the mission without any problems, even can play online on some servers. But now my game is crashing on every wasteland server when loading the mission. I've added a new zip file with files from appdata\local\arma 3 alpha folder.