IMAP Sync delays

I am looking at using eM Client as a replacement for MS Outlook.  I have successfully set it up to use my BT/Yahoo email account and my iCloud email/calendar/contact accounts. However, I am having a problem with the delay in syncing IMAP folders.

For example, if I send myself an email from my iPhone, it appears in my iPhone inbox and BT webmail inbox within a few seconds. However, it can take anything up to 30 mins to appear in eM Client, even if I manually refresh.

Another example: if I move a message from my inbox to the archive folder, it obviously shows that move straight away in eM Client but, again, it takes a long time before that change is reflected on BT webmail or iPhone.

I don’t know if it’s related or not but the Operations window shows almost constant synchonisation of subfolders. There are no errors displayed in the Operations window.

eM Client version 7.2.38732.0, Windows 10 Home version 1903