Missing Messages

On my Mac running 10.10.5 and Mail 8.2 I find that many messages that appear in iCloud or my iPhone don’t appear on my Mac.
Sometimes they appear after a few hours, others as many as several days.
I have another admin account where I have no plugins installed on my Mac and all messages are there

Does Spamsieve have anything to do with this. Hos anybody seen this behaviour?

I don’t think so—it only looks at the messages after they’ve been received. You could try temporarily removing any plug-ins (including SpamSieve) or rebuild your Mail database.