can't flash stock rom after Bootloader unlock

[salsabreak]

Hello,

after I unlocked my bootloader I was able to flash TWRP and LineageOS.
But now I am stuck on it I cant flash back to a stock rom.

This is the output of latest flashtool:

26/047/2017 13:47:04 - INFO  - Loader : S1_Root_f936 - Version : MSM8994_50 / Boot version : S1_Boot_MSM8994_LA1.2.3_45 / Bootloader status : ROOTED
26/047/2017 13:47:04 - INFO  - Max packet size set to 4M
26/047/2017 13:47:04 - INFO  - USB buffer size set to 512K
26/047/2017 13:47:05 - INFO  - Parsing boot delivery
26/047/2017 13:47:05 - INFO  - Ending flash session
26/047/2017 13:47:05 - DEBUG - Writing packet to phone
26/047/2017 13:47:05 - DEBUG - OUT : CommandID : 4 / Flags : false,true,false / Data length : 0 / Data CRC32 : 00 00 00 00
26/047/2017 13:47:05 - DEBUG - Reading packet from phone
26/047/2017 13:47:05 - DEBUG - IN : CommandID : 4 / Flags : false,false,false / Data length : 0 / Data CRC32 : 00 00 00 00
26/047/2017 13:47:05 - ERROR - null
26/047/2017 13:47:05 - ERROR - Error flashing. Aborted

I tried different USB ports reinstalled drivers and different ROM Versions.

Any idea why this always fails?


Update: It works with an older flashtool version