Odd Shift in Font Size in Messages

I occasionally receive messages from colleagues in which the font size shifts strangely from my standard, 12 point to a tiny, almost unreadable font.  Checking the same message in Gmail, there is no such shift. See image below (names changed to protect the innocent.)

Help appreciated!

I’m using the lastest version of eM Client 6 (Pro and free), with an imap Gmail account.  Thanks!

Hello,
is this a HTML or Plain text message?
Could you perhaps Forward this message to me as attachment for inspection to rust@emclient.com with a link to this forum topic?

Regards,
Olivia

I just sent two examples, in separate emails.  Thanks for taking a look!

Hello Lance,
unfortunately the issue is not in eM Client but with the messages themselves - they have a mixed formatting.
The first sentence/paragraph has no set formatting, so the eM Client’s default font size will apply. The rest of the message has the font size set to 12px (pixels being a pretty bad size element choice here). 
I guess that gmail does not recognize this mixed formatting and changes the message to Plain text (removing all formatting) by default, while eM Client just views the messages as it is.

If this happens to most/all messages you receive in eM Client, it might be best to set all messages to be shown in Plain text in the Menu>Tools>Settings>Mail>Read section.

Regards,
Olivia