I get a random connection error when trying to upgrade a wall with manuals

[The greater]

I just got some wall upgrade manuals and when I tried to upgrade I get a connection error and had to restart the game

 

[nobodyknowsthetrouble]

That is ‘normal’.
This often happens if you want to improve more than one wall -> better upgrade one at a time.

Alternatively, try clearing the cache; this solves many problems (but only if your account is somehow saved, e.g. connected to dw)