Strange things happening with TB 156.0b3 (32-bit) and Yahoo

I've been using TB for years and all has been working well. But now I have no idea what is going on. When I try to download new email from my Yahoo account (using pop3) it tells me that it is downloading 1 or 25 (say) and none get downloaded. Then I delete some emails in TB and a little while later those deleted emails get downloaded again but none of the latest emails. Even if I logiin to Yahoo and delete those emails, TB seems to manage to download them again. How? If I delete the first email it should download sometimes the rest will download but not always. Sometimes when I update to the latest version of TB emails start downloading. I have tried to doing a repair on the Inbox but this seems to make no difference. I've no idea what to try. Anyone got any advice/suggestions? Also, how do I get from the Beta version of TB to the stable version? I don't even remember choosing to use the Beta versions. Lastly, I often get pop-up messages saying that folders cannot be compacted because something is using those folders. I've never understood why TB puts out this message. Why does it not just compact the folders when it has done whatever it is doing? Is there a way of stopping these messages and finding out what is using the folders?