[Galaxy S III Original Android Development] curiousrom:
TWRP Recovery Update, Clean Install & APN T-Mobile

"...thanks again" - Thanks for the thanks & hit the :good: Thanks! button on the posts that you find helpful. Besides being good for the ego of the poster, it indicates to other users that the suggestions/tips were useful to somebody so may be good for them too.

All your APN misadventures got my eyes glazing over. :eek:

The art of troubleshooting is systematically eliminating possibilities one by one. If you do too much stuff before reporting here it's hard to troubleshoot.

Because you flashed so many ROMs including one that is not for your device (risky), report bootloop with Archidroid & you report Lineage browser errors & crashes I suggest a systematic clean slate install from the ground up.

Going back to your post here I see in your TWRP attachment with errors: TWRP v2.8.6.1 which is an old 2015-03-30 and that could explain "unknown command" errors which can lead to all sort of problems in the OS & booting problems.

Post #1 in this thread says: "Update your recovery... TWRP... you need 3.0.2-2 or higher to automatically install updates in Lineage 14.1".

1- Go to the TWRP for i9300 download page and get the most recent .img version (currently twrp-3.2.1-0-i9300.img 2017-12-09), copy to external SD card, boot in Recovery, flash using TWRP & reboot in Recovery as per TWRP Install (Requires TWRP 2.8.4 or higher already installed) instructions.

BTW you can take a screenshot in TWRP with: press volume down first & tap the power button. It will save it in > external SD card/Pictures/Screenshots instead of taking a photo of your phone's screen.

2- Flash modem...zip with TWRP & reboot in Recovery. (optional if you are currently in stock T-Mobile you could keep that modem for now, note the > About phone > Baseband model and can back it up with the Partitions Backup app > Radio)

3- Follow exactly this guide: How to wipe in TWRP properly? & reboot in Recovery.

4- Installing LineageOS from recovery part of the wiki including steps 10 (gapps ARM Android 7.1 first, choose your Variant) & step 11 for Lineage su addon addonsu-14.1-arm-signed.zip (after gapps). Reboot in System, let the OS stabilize for a few minutes before logging in your Google account (if you have one) via Wifi.

5- With cellular data enabled & disconnecting Wifi the phone should normally detect the network & setup the APN according to the SIM. If you see a bunch of APNs from other brands like you described, I can't explain that. I have none of those, only the one for my current network operator. If you don't want to delete them, then press on each of them and toggle APN enable/disable to disable all the unwanted one. That should prevent the OS from defaulting to the wrong one.

6- If you still don't have cellular data then maybe follow the official T-Mobile APN Settings Support page: > Android APN settings > APN: ...epc.tmobile.com (for non-LTE devices) & all the other settings in that Android chapter. Pray if you are a believer & enable cellular data. If it does not work call T-Mobile & give them hell (politely). Edit: maybe you can edit an existing T-Mobile APN instead of creating a new one?

Edit: If you already flashed the modem you could try flashing back the modem from the stock T-Mobile Samsung ROM you downloaded. If using Windows unpack the rom with 7-zip of similar, copy modem.bin to the same folder where you have my flashable modem_CWM_I9300UBUGNK1.zip and drop it over it. It should replace the modem.bin inside & you can flash that .zip with TWRP & reboot. If you try to unzip/re-zip that modem special folder it will not be flashable anymore I think.

7- Don't worry about the MTP Host crashing, it's a known LOS for i9300 bug & is used only when connecting other USB devices to the i9300 via a OTG cable making the phone a USB host. Settings > Apps > 3 dots > Show system > MTP Host & Disable the thing. No side effects whatsoever when connecting to computer or anything else for me since several weeks.

Good luck & report back.