@joyously
The site is multisite network setup with about 50+ sites.
(not-a-migration nor change from single site to multisite network)
Few plugins needed update
- Webcraftic
- Popup Builder
- Meta Box
- HubSpot All-In-One Marketing – Forms, Popups, Live Chat
- Contact Form 7
- Cloudflare
The changes in permalink was noticed after an hour.
I do suspect the error is caused by
- some sort of filter applied to the output
- some malware got into server
- cloudflare?
Checked malware with false positive reports