Text style impossible to control

output

As you can see in the gif it happens all the time that I cannot control and have consistent formatting when composing emails in EM Client.

The first word is shown as Helvetica 14 as the second one which does not at all correspond to what is seen.

I fear that the application is shuffling styling and text zoom which results in non manageable formats.

Even if I apply Zoom / Original it does not solve the issue.

Any hint?