I wanted to make some changes to my odoo setup after more than a year of use. I'm trying to install new addons but when I place some of them in the addons folder the server stops working properly. The webpage still loads but some images are missing and when I switch to developer mode the web page is completely unusable. All this happens without installing the addon inside odoo only by placing it on the folder.

I'm not sure if its a problem from the addon as I have the same problem with different addons that I've tried to place individually to find which of them was causing the problem and I have more than one that when palced individually produces the same result. 

I've checked the log files but I can't find any error displayed, even when using log-handler in DEBUG mode I can't see why it's failing.

I also found that when I remove the plugin from the folder and restart the service (I'm on Ubuntu 16) odoo works fine again.

Any idea on how to find the problem?

Thanks