filter hint route to master , can't send 2 requests

Hello,

We recently migrated from 1.3 to 2.3.7, and our application is/was using the filter hint
'-- maxscale route to master' on some requests.

Under 2.3.7, we noticed that it works for the first mysqli request, but if we do another request just after, we got a NULL reply.
The db handle is also showing a sqlstate = #HY000. (not immediatly after the first request, but just after.).

So, if we use a hintfilter, we are obliged to call again a mysqli_connect (this was not the case under 1.3.)

Not sure if it's a bug or something new, is there a way to fix this ?

thanks in advance,