I had this all the time when connection was slow and more than 100K files uploaded to servers.
The error name Connection Timed Out had popped up in the middle of upload process after progress bar showed 100%.
No, it wasn’t the server caused the problem. That wasn’t Passive Connection problem, which also could Connection Timed Out. This small problem can trick you. You think the server do it, but it isn’t.
The solution is simple. Open FileZilla > Edit > Settings > Timeout in seconds, default is 20, change it to a higher value like 300 > OK
Simple. isn’t it?
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Still not working
I even changed it to 1000.
What your FileZilla said about the errors?. FileZilla errors could hint what your FTP problems. It could be the server settings. It is not always caused by FileZilla