How to debug X-Magento-Cache-Debug MISS

Question

I have one site with FPC cache enabled that is always returning MISS in the X-Magento-Cache-Debug header.

How can I debug "who" is marking the homepage non-cacheable?

So far I checked the usual suspects:

• Caches status is enabled including FPC cache.
• Tested with and without Varnish
• Checked all the source code for the modules searching for "Cacheable = false" and isScopePrivate = true and for debugging purposes changed them to "Cacheable = true" and "isScopePrivate = false".
• I disabled third party modules, run a setup:upgrade
• Changed to developer mode, cleaned caches, recompiled

So, the thing is, is there any function where I can put a piece of log to determine who is "voting no" to have a cache?

Magento version is 2.3.5 p1

• Rahul Barot: Are you using any custom theme? Have you checked in theme that cacheable=false is not written there. Also is there any third party modules which are located under vendor? Did you checked by disabling them also?
• Amit Bera: On first request, the page will be cache hit miss and then from second hit , we see see X-dubug hit

Answer 1

update

After extensively checking that cacheable=false was not written anywhere I found that a plugin (mageplaza bettermaintenance) was incorrectly setting "noCacheHeaders".

So, next time, after grepping for "cacheable=false" I'll grep for "setNoCacheHeaders" as well.

https://github.com/mageplaza/magento-2-better-maintenance/issues/24