Symfony version(s) affected

4.4+

Description

WhenHttpCache is allowed to preserveLast-Modified (see#42355) clients will execute subsequent requests withIf-Modified-Since. If cache then returns a304 Not Modified this will result in an exception.

This cycle will continue:

• Request: initial
• Response: sucessful, cache store,Last-Modified header
• Request: withIf-Modified-Since
• Response: 500 (client drops cache), error page
• Request: initial without timestamp
• Response: sucessful
• …

How to reproduce

Merge PR#42355 or check outhttps://github.com/aleho/symfony-httpcache for a minimal demo.

Possible Solution

No response

Additional Context

No response