I just did some test where I move large number of files between folders, cleaning up the structure.
This experience was not very impressive I’m afraid. I’ll concentrate on the serious bug here.
When selecting one or more mails and then using the “move to folder” function it takes a few seconds for the list of selectable folders to show up. When repeating this with more mails right afterwards it takes even longer (4-6 seconds). Keep repeating this like moving 20 mails at a time from one folder to the next text increasingly more time, before the windows goes white, and nothing works (Can’t log in, in a different window or browser, like the server freezes. After 2-3 minutes waiting I could log back in, but some of the changes I did like 10 minutes before was undone. 
This behavior was reproducible, but only at random, which leave me to believe it’s server/syncing related. It’s seems to be more a function of how often I use the “move to folder” function, more than the number of mails I move per time. (Also sometimes there is notification showing center bottom of screen saying “Syncing 0 / 28” for example, counting upwards about 1-3 per seconds, but then skipping back to 0 over and over again)
(I can’t find any way to move all mails in a folder to a different one any other ways, am I missing something? Pressing CTRL+A should select all mails in open folder imo, now it just select all text except mails, which is pointless.)
Related: When trying to log into RB7 while I made the server unresponsive (same tab, new tab, new window, new browser; all the same behavior: I just get a white screen while I wait for the server to respond. A error message would be appreciated, so I knew it was not a browser issue.
Sorry if I sound very negative when reporting bugs, I really appreciate what you’r building here!
I’ll update the tread if I find any patterns, I’ll do some more testing.
edit: I think I broke something; I can no longer delete folders, and everything is super slow… hmm.
Ill try again on a different machine when I get home. It says it’s done syncing too…
edit 2: Issue reproduced on different machine, after 6th “move to folder in a row” in freezes. After syncing has caught up (waiting a few minutes) I still can’t delete folders any more. Delete confirmation message shows up, but when pressing “yes” the folder stays (on all devices).Any drag-and-drop or “move to folder” operation remain super slow, freezing for several minutes, even if I wait a long time first.
edit 3. Regarding the “can’t delete folder” that is not an issue. It just happens that the last folder I wanted to delete, and waited because I needed a folder to move files to and from for testing, was also in an old filter. As soon as I deleted the filter I could delete the folder. There should of coarse be an error message to inform me what was going on instead of it just not working, but that is not related to the freeze bug.