The folder on Android is set by default to Send Only, meaning that it can only send modifications and deletions from the device but cannot accept any modifications or deletions done on other devices. If you prefer to have it sync two way, then you should change the folder type to Send and Receive.
Please check the Getting Started guide in the Docs if you want a brief overview of Syncthing itself, different folder types, etc.
Also, please do not click the Override Changes button unless you are 100% sure about it and understand what is going to happen after doing so.