AEM 6.5.6 (upgrading from 6.5.3) can't save component dialog

I was troubleshooting an issue after upgrading to 6.5.6 from 6.5.3 and still can't figure out why so though I would ask for your help to see if someone is also experienced the issue and got a workaround or so.

Background:
- Issue happens after I upgrade AEM to 6.5.6 from 6.5.3
- ACS common version is 4.0.0
- Core component version is 2.8.0

Issue:
- When saving any component dialog (even the default one by we-retail), the value didn't get saved into the page jcr:content node but it gets created in /libs/cq/gui/content/editor/content,

for example, if I modify this page /editor.html/content/we-retail/us/en/experience.html

then instead it saved to /content/we-retail/us/en/experience/jcr:content/...

actually it got created in /libs/cq/gui/content/editor/content/we-retail/us/en/experience

as a result, when opening the dialog again on the page, it will show no new value.

What I noticed, when submitting the dialog, the POST request makes to aem are different between fail and success case.

E.g
Wrong case:
request URL is posting to http://localhost:4602/editor.html/content/we-retail/us/en/experience.html

(the page itself is incorrect)

Correct case:
request URL should be posted to
http://localhost:4602/content/we-retail/us/en/experience/_jcr_content/root/responsivegrid/text

I got no error in error.log.

Solution:

Please check and see If you have custom XSS rules? Check if the overlay exists: /apps/cq/xssprotection/config.xml.

If yes, move the overlay to tmp and test again.