Web Clipper stopped working on one specific site

Operating system

macOS

Joplin version

2.14.20

Desktop version info

Joplin 2.14.20 (prod, darwin)

Client ID: 04e734b2968e4b3496eda765784029a1
Sync Version: 3
Profile Version: 46
Keychain Supported: Yes

Revision: cfd98e3

Backup: 1.4.0
Bidirectional Links: 0.1.2
Font Size Shortcut: 1.0.0
To Google Search: 1.0.0
Zotero Link: 1.0.2

What issue do you have?

I have a specific set of websites from which I take clippings, using `Clip complete page (Markdown)´.
Suddenly, on one of those sites clipping no longer works.

The plugin shows:

"Processing note... The note will be available in Joplin as soon as the web page and images have been downloaded and converted. In the meantime you may close this popup."

Nothing happens, plugin fails silently, no errors.
Tried HTML clipping, also fails.

Is there a way to debug and discover what is going on?

macOS High Sierra 10.13.6 (17G14042)
Joplin 2.14.20 (prod, darwin)
Waterfox G6.0.13 (64-bit)
Web Clipper 2.11.2