Same issue here on my friend's vanilla 7d2d server and A20 experimental server. We noticed that the " falling through the map" and "can't use "E" " errors correlated with very high ping spikes on my end (20K plus), which we originally thought was caused by my distance to the server. I've since uninstalled AVG antivirus and disabled windows antivirus, thinking that some real-time file scanning was happening. It seems to have helped, though I'm still testing. I also set my video settings to lowest and turned v-sync off. So far so good.
Re: A20, my player files keep getting corrupted server-side for some reason. After wiping everything related to 7d2d locally and reinstalling several times, I still got the error. So my friend deleted my player files on the server. This let me get back in (as a beginning character), but in a couple of days I was getting red code error spam, and my character was dropping everything on death (server has that disabled). Shortly after I couldn't launch game...was hanging on "creating player" again.
One final mention, is that after doing a full reinstall, start a local game first, before joining multiplayer. Anyway hope you get things sorted out, its really fristrating huh?