I can't help you with this specific problem, but I know you'll get decent advice from the DC-Unlocker people via their chat; the big Message button on the bottom right of their site starts a conversation. If it's outside their business hours (GMT+2), you'll get an e-mail and the conversation will continue that way.
Last week, thanks to the recent revival of this XDA thread, I tried to resurrect my old Y550-L01 once again. About two years ago, I somehow bricked it hard. Now, this made me contact the DC-Unlocker people and use their DC-Phoenix software. It all looked very promising (downloading the stock firmware, bootloader, etc. from their servers, detecting the device both in some kind of fastboot mode when an SD-card was inserted, and Qualcomm HS-USB QDLoader 9008 mode when not).
The flashing failed repeatedly, so I chatted with them. Followed their advice, and chatted again. Followed their advice and mailed some logs... All to no avail. Their conclusion was (as is mine, and was ours in this thread, two years ago): the motherboard would have to be replaced to revive it. For me, that's not an option, so I handed it over to our city's recycling facility. I put a printed note inside pointing to this thread, so that anyone who tries his/her luck with the device, won't have to start from scratch.
TL;DR: seek out the assistance of the DC-Unlocker people; I spoke to and mailed with Waldmeras and he was very knowledgeable and friendly.
Good luck and kind regards,