Finally found the problem:
Sonarr fails on taking the backup, hence not proceeding with the update. The problem here is that the zipping process is finding an invalid language. Although the profile is set to English, the process is still failing. The problem lies here: the service is running on a system level not on the profile itself.
An easy way to fix this is by stopping the windows service by doing the following: Run > “services.msc” > nzbdrone > right click > stop > right click again > properties > log on tab > log in with the profile account > start service again.
Another way to fix this is to actually change the system settings of the Windows Machine to English. This can be done from Control Panel > Region > Administrative Tab > Copy Settings.
A restart for both of the above may be required.
Jake