Installing LineageOS on a One Plus X E1001 (not E1003, I believe E1001 is an Asian version whereas E1003 was old in Europe) was a bit painful. This article will not repeat all instructions to install LineageOS on One plus X (which can be found here: https://wiki.lineageos.org/devices/onyx/install) but only cover some unexpected behaviors I need to circumvent to install LineageOS.
First no recent (3+) TWRP version was running fine: all refused to boot (fastboot boot path/to/recovery/file.img) with the following error message:
Remote: dtb not found error
I had to use an old TWRP 2.8.7 version to make it work. Here is the version that worked fine for me: twrp-184.108.40.206-6.0-onyx.img.
Then, the LineageOS zip file could not install because of the following error message:
Comparing TZ version TZ.BF.2.0-2.0.0137 to TZ.BF.2.0-2.0.0134 assert failed: oppo.verify_trustzone("TZ.BF.2.0-2.0.0137") == "1" E:Installation aborted.
To fix this one, I had to first flash the firmware/bootloader with a more recent version. Installing the following file with TWRP did the trick: OPXBLUpdateOOS3.1.zip.
After that, LineageOS (one of the nightly version of May 2018) installed just fine.
I hope this will help some people facing the "dtb not found" and "assert failed: oppo.verify_trustzone" error messages!