Mail trained as spam re-appears in inbox seconds after having been moved

Hi,

My set up is:

MacBook Pro Retina (late 2013)
MacOS: Mojave 10.14.3 (18D109)
Mail client: Apple Mail 12.2 (3445.102.3)
SpamSieve 2.9.35

The issue is with my Google inbox in Apple Mail, that is my Gmail account, other inboxes (all IMAP) move the messages trained as spam to to the Spam folder ‘On My Mac’ (i.e. a local folder) as set up via the Apple Mail plugin and all works well like it has done for the last many years of trouble-free SpamSieve use. However the Gmail account moves the message trained as spam and it disappears from the inbox as it should (and the other accounts do), but then a few seconds later it re-appears.

As I said everything has worked fine for years, including my Gmail inbox, but recently (probably since upgrading to MacOS Mojave) Gmail has had this issue.

Is it because the Gmail inbox is on Google’s servers and the ‘Spam’ folder is on my Mac?
Is it because of Mojave, some new security pain in the arse?
Is there a fix?

Any help appreciated.

Thanks.

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