Yahoo folder with more then 300.000 messages never stops sync

I have a yahoo account with a folder with over 350,000 messages.

I checked this folder to download and keep messages for offline use.

After a long time downloading, the number of messages has stabilized, but synchronization continues and never stops.

What could be wrong?

After downloading the headers, that will give you the message count. After that, the application is downloading the message content and attachments for off-line use. Depending on the size it could take some time.