What is stripping URLs from some emails?

[StuartR]

Some URLs are disappearing from incoming emails in Outlook, and I can't work out why. There is no indication that this has happened, but the URL is definitely not there.

I collect the same email, from the same POP3 server, on the Samsung email client on my phone and the URLs are present.

This doesn't happen to all emails, the one that I noticed this morning was included in a table that just had a single cell with some text that was hyperlinked to a web page. Other URLs seem to arrive quite normally.

I can't see any add-ons or rules that could be doing this.

Any thoughts on how I could troubleshoot this?

[StuartR]

A possibly related issue is that some emails display this error message, after I allow Outlook to download images

This same email displays correctly in the mail client on my phone.