My hint to you @dreamsoft:
Rollback to 3.6.4!
This new UCSS and Guest Mode is worthless at this stage, they modify all the engine to generate a Critical CSS path in a new way who ends consuming a lot more bandwidth, stress more their and our servers and breaks our websites. Quic.cloud credits empty in ours (free accounts) and this lets your site with a broken CSS. Unbelievable!
If you have a very small wordpress site, with a lightweight content, well you don’t see most of problems… but the majority of users here will suffer with this new and broken update.
Rollback to 3.6.4 or find another solution until devs at least assumes the mess they made in this update…