So…
Actually, there’s a config property in AHC for enabling relative uris when talking to an SSL proxy.
If the behavior has changed, it might be that I clean up that code and accidentally fixed it (sic).
It’s disabled by default (will have to talk with other AHC committers to know why).
Sadly, it’s not exposed in gatling.conf… but the good news is that you can set it with a System property.
Until I get this fixed/decided, please add this line in your simulation (or add the property from the command line)