Missing text when sending reply from kmail

Good morning

I've noticed in the last couple of days when replying to a friend that any 
text I write within a short distance below the quoted (replied-to) text is 
missing from the email that actually gets sent.

I've used the browser in Akonadi console to verify that the text just isn't 
there, as if I didn't even type it.

Before I go through the tedium of trying to troubleshoot this, does anyone 
know whether this is (or has been - I'm on Plasma 5.18.6) a known issue? 
Thanks in advance.

Kind regards,
Huw

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