Meta description excerpt not showing

Hello.

Thanks to Yoast SEO, the excerpt of each article should be auto generated for the meta description. Actually, I can see the excerpt of each articles in the meta description in “view page source” (about 155 characters / 25 words).

My problem is that the excerpts do not show in the snippet. I get this message: Please provide a meta description by editing the snippet below. In the meta description box, I see: %%excerpt%%

I have deactivated ALL plugins.
I switched theme to Twenty Seventeen
I kept Yoast activated as it is required to auto generate the excerpt (my issue)
The issue remains; the excerpts are not there (but it is in the “View Page Source) !!!
Have you heard about this problem before? Do you have any suggestions on how to fix this?

Thanks in advance for your help.

MART

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