At home I've returned to my default network settings and everything is still working fine.
So the problem with synchronization could be some kind of "lock" on the server for a specific account AND it is related somehow with Network Address Translation in situation when translation is many to one (many private addresses to one public address). I think, that an additional condition for the "lock" bug is a presence of more than one computer with Evernote app running in the network.
In my situation the "lock" happened in my home network (30Mbps Ethernet) and in my office network (>100Mbps Ethernet) as well. In my home network there are three laptops with Evernote app while in my office a tens of laptops with Evernote app may running. When I've "unlocked" my Evernote app by changing the IP address in my home network then in the office I was "unlocked" too.
Summarizing: I think that for everyone with a similar situation there are two solutions. I don't know if you are familiar with networking, so I assumed that one solution will be "difficult" to some users, while the second one should be much easier:
1. The "difficult" one: Close the Evernote app and then change your IP address. For example if the DHCP server always gives to your computer address: 192.168.1.12 then try to use any other FREE address in this network, for example: 192.168.1.15. Then test your connection. If you can browse the Internet, then run the Evernote app. It should synchronize fine, and you should be "unlocked".
2. The "easy" way: try to use Internet in any new place - it should be a new place for your laptop, not for you But remember that an open, public WiFi hotspot is not the best solution because:
- using an open, public WiFi is not a secure and recommended way of connecting to the network (unless you exactly know what you do)
- potentially, you have a lot of new notes to synchronize, so the fast and reliable connection should be your choice.
I hope it will help you.
PS I'm sorry for my bad English - I'm still learning