Please update to the latest Anki version then try again.
When I use older version(2.1.26) its okay, but when I update it, to （2.1.29）it seems anki have a different data format and sync strategy. And I think maybe the new strategy can’t use the system proxy, and I tend to use proxy to get internet. when I close the win10 set of proxy, it can work normally.
It seems can be solved by set [ environment var], but I don’t know if it have the option to set the proxy and choose IE proxy.