re-locked Fairphone 3 won't start after installation of /e/-OS and TWRP

Hi.

So I managed to put /e/ OS (by doing the HOWTO on docDOTeDOTfoundation/devices/FP3/install ) and TWRP 3.4 (by doing the HOWTO on twrpDOTme/fairphone/fairphone3.htm ) plus doing a 'fastboot oem lock' and a 'fastboot oem unlock') on my FP3.
As long as I keep bootloader unlocked it starts /e/ OS on power-on or TWRP when I power on with holding PWR and volume-up.

However, when I lock the phone all I get is a:

Read more