Could it be that they are Google Online Fonts?

No they are not google fonts

These are the fonts, they used to be no problem, I also tried with other common fonts and get the same

Bernard, there is a problem adding fonts the way you are doing it. Whilst I cannot explain why they may me disappearing, you should be aware that these fonts (if embedded in the website) will only be seen by Windows users, if they are not being embedded thay will only be seen by you.

Have you tried using the equivalent google online fonts? I am sure you will produce a better and more reliable website.

I just set up 2 Google offline fonts with Website X5 Evo 2022.3.4 locally.

>> https://google-webfonts-helper.herokuapp.com/fonts

I first set up the "Comfortaa" font locally, exported the website, closed and restarted the program, then set up a 2nd Google offline font "Lato" locally. Then closed and restarted the program, the two fonts are still present in WebSite X5.

Each Google offline font consists of 5 font files, of which 4 font files are inserted into WebSite X5.

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Using google fonts would be good, unfortunately these fonts are embedded in many of the PDF files I have on my site, these are from another company so is not easy to change.

I am adding the fonts as directed in website X5, this problem only apeared after upgrading to this latest version...

Maybe I will try to uninstall and reinstall website X5.

I restarted my notebook und the two fonts are still in the WebSite X5 font selection.

If the Google offline fonts are integrated the same way as mine and they disappear again, then the problem must be on the computer and not on WebSite X5.

To be on the safe side, you can reinstall Website X5, possibly several times, to rule out installation errors.