Problem with Content of Contact Form

I am using the RapidWeaver default contact form on three websites, the last of which was set up a few days ago…
Mail is reaching the mailbox at my domain - at least to / from / subject line are reaching me.
However any body text is rendered like this:

DQotLXJtcy1taXgteDg4 (that’s the first few characters only - goes on for about 19 lines full width of my gmail window.

I can reply to mail and ask sender to repeat their question / comment - so that suggests settings are correct.

Mail sent direct to the same email address goes through with no problem at all.

I have two other, very low traffic sites. On both of these the form used to work, and neither of them do now either. As near as I can judge, the problem arose mid Jan, but I have only noticed on testing of the new website.

We have tried utilising the form in Chrome and Safari - same results.

Hosting is with EZPZ. and I use Rapid Weaver 5

Any ideas please?
Thank you