HTTP Caching problem. Request works on and off - apache

Question

I'm facing a weird behaviour on chrome with http get requests that most likely has something to do with cache.
Basically, the same request returns 200 the first time, then if I send the same request again by entering again the URL bar it returns 404. THen again 200. Then 404.
The request looks something like this (by using the dev tools on chrome) I use ## to hide sensitive info
General:
Request URL: ###
Request Method: GET
Status Code: 200 OK
Remote Address: ##############
Referrer Policy: strict-origin-when-cross-origin
Response Headers:
Accept-Ranges: bytes
Cache-Control: max-age=0, no-cache
Content-Length: 75209
Content-Type: application/json
Date: Fri, 10 Sep 2021 10:29:22 GMT
ETag: W/"IDGfBPV6nmAIDGefDH3A0M"
Last-Modified: Wed, 08 Sep 2021 08:36:01 GMT
Server: Jetty(9.4.z-SNAPSHOT)
Request headers
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate
Accept-Language: en,it-IT;q=0.9,it;q=0.8,en-US;q=0.7
Connection: keep-alive
Cookie: ##################
Host: #########
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.4577.63 Safari/537.36
If i now press enter in the URL bar issuing the request again i get the following response:
General
Request URL: ####
Request Method: GET
Status Code: 404 Not Found
Remote Address: ######
Referrer Policy: strict-origin-when-cross-origin
Response Headers
Cache-Control: must-revalidate,no-cache,no-store
Content-Length: 347
Content-Type: text/html;charset=iso-8859-1
Date: Fri, 10 Sep 2021 10:29:05 GMT
ETag: W/"IDGfBPV6nmAIDGefDH3A0M"
Server: Jetty(9.4.z-SNAPSHOT)
Request Headers
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate
Accept-Language: en,it-IT;q=0.9,it;q=0.8,en-US;q=0.7
Cache-Control: max-age=0
Connection: keep-alive
Cookie: #################
Host: ####
If-Modified-Since: Wed, 08 Sep 2021 08:36:01 GMT
If-None-Match: W/"IDGfBPV6nmAIDGefDH3A0M"
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.4577.63 Safari/537.36
And so on, 200, 404, 200, 404 ...
Differences I noticed are in the Cache-Control header of the response and the new If-Modified-Since and If-None-Match request headers.
The backend server is a proprietary server and between the client there is an Apache Proxy Server.
I know that to get the solution I should provide more data (maybe the httpd configuration) but I'm more like trying to understand what the issue is rather than asking for a magic solution.
I searched on google "Get request works on and off" and all sort of wording variations but had no luck.
If anyone could help me out at least understanding the problem
Thanks
Davide
UPDATE
As Kevin suggested in the comment, shutting down the apache proxy did not change this on/off behaviour. Has to be something within the origin server