Looking at the betaflight code it seems like these pins are active high, so the last build is probably the correct one. But no idea why it doesn’t work.
I just retried to resoldered it, reboot the flight controller, and it works !!!
I think I forgot to reboot the flight controller after I changed some parameters.
Sorry for that 
Thank you so much !!!
Great! So which options and which firmware worked - it’s important that I get the right ones here for the PR. Does it work without setting SERIAL3_OPTIONS?
So here is the full parameter file : flyball_r7008sb_receiver.param (18.1 KB)
And I just tried to set SERIAL3_OPTIONS = 0, and it seems to work too !
This is all with your last firmware.
Great!
Please can you try this final build with SERIAL3_OPTIONS = 0 just to confirm I haven’t broken anything. I noticed a little bug in the uart code.
arducopter.zip (615.5 KB)
It’s working too with SERIAL3_OPTIONS = 0 
Great! I will cook up a PR.
Ok nice ! Thanks again, you saved my day !
The PR from Andy was included in Copter-4.1.0-beta8 so hopefully this item is all resolved now. I’ve marked the item as resolved on our 4.1 issues tracking list but please tell me if it’s not. txs!