[Android Q&A, Help & Troubleshooting] pndwal:
Hi Jon.

I've addressed most of your concerns so please read the following carefully.

Well done with your efforts so far. Very interesting that you have B249 on L02 and unlocked bootloader / loaded TWRP / rooted successfully. We thought it might be impossible to unlock if updated beyond B247 as it seems Huawei updated XLoader on some Y550 devices with B249. See my posts #6401, 6534, 6510 here.

Please tell us more re how you unlocked. What is bitunlocker? (Links please). How recently did you unlock bootloader? Thanks.

Modem baseband update and original stock image files are included in Y550 "Development" thread, post #2. Link at end this post (See Files and Tips).

Just flash 'modem' update to 11060045 for any custom ROMs, and flash 11060009 if returning to stock. No need to extract from your device. Also, modem baseband images are for all models even though physical radio comms differ per region sold (no 'global' model was available when this phone was made).

Factory reset is a wipe of all user data and whatever ROM you have will remain. Do not confuse this with flashing factory Stock ROM.

Flashing stock ROM may be needed at times to fix problems when they occur inexplicably or thru messing with apps/ mods that affect partitions other than those contained in custom ROM, or accessed by TWRP (there are many partitions other than what you see in TWRP set up by OEM and included in Stock ROM.)

For example, using OctOS you may experience this: phone suddenly won't boot unless SIM card is removed. Factory reset doesn't fix it, but restoring stock then reflashing OctOS does.

Stock for a number of regions available here:

http://huawei-firmware.com/phone-list/huawei-ascend-y550

L01 is your physical model variant with its peculiar set of radio bands for networks. B239 is simply stock ROM version, and earlier versions can usually be restored, but updated bootloader (XLoader) (as some got going from B247 to B249) and 'anti-rollback' can prevent downgrading to these. You cannot convert L02 to L01, and factory reset leaves ROM intact.

I wouldn't suggest using older OctOS ROM unless you really need Nato's custom Soviet kernel mods, eg OverClocking, QCom Quick Charge etc. His kernels were customised to work with likes of Kernel Aduitor, and many tweaks were available.

However current LOS is much more stable although modifying kernel level features generally don't work even if they appear to be set in KA. In fact these are the usual cause of 'Black Screen Freeze' problem. Also, being up to date with latest LOS sources we have up-to-the-minute security patches courtesy of [MENTION=7866480]fwiep[/MENTION] at present.

Adopted Storage:

You need native Adopted storage for Y550!

Well, there is. See my notes below regarding migrating data and apps. Seems you haven't done this. You would have been presented with this option when first formatting SD for Adopted Storage.

Find option in Settings, Storage, select SD Card, click options (3 dots at top), click and accept Migrate data (and apps). Or, format SD as Adopted again in settings, and accept move / migrate data and Apps when prompted.

Note very useful developer option 'Force allow apps on external':

Further Regarding GApps:

The problem is Y550 has only 989MB accessible system partition (even though total size is 1.2GB), which is small, and messing with partition sizes is perilous (only for masochists!) I have 171 MB free after integrating system updates, and I flash nano GApps which is 215MB, so you may be able to flash micro (246MB, Ie 31MB extra) or possibly mini (378MB, Ie 163MB extra), but this would leave practically no headroom, and I'd be keeping 100MB or so free for updates etc.

Full GApps is 627MB, and stock is 752MB, so these are a no go on Y550. It is a budget phone after all, though arguably the best yet :)

TWRP - you need unofficial version to flash ROMs on L02. Bit of a pain, but both have different features working: