TAKE NOTE!!!
At the very last leg of his quest, if you ask him "You still need help?", it will LOCK OUT the option to give him the Repeller Coil!!!
Do NOT ask him if he needs help until AFTER you hand him the Repeller Coil!

Absolutely CLOWN WORLD game design to just not automatically give him the Repeller Coil AUTOMATICALLY when you ask him this question.. FFS Deck13...

I do everything right, get 2.0 weapon & implant, choose to stay and don't get the "say goodbye" prompt before heading above to start the train??? I start the train, get no cutscene but Warren contacts me saying we'll meet again to say "goodbye". I go back down to him and get no new options WHAT THE HELL??? Reverting a save and retrying doesn't fix it! I really enjoy the Surge games but inconsistencies and bugs are really making me not want to do new game+ or play future entries... Anybody experienced this scenario and fixed it?

Maybe this will help somebody on console with something I found out much too late. NEVER save at a medbay in this game unless you are 100% sure you got the outcomes you wanted! This can even be hours of gameplay if you are unsure what to do. If you mess up anything just quit to menu and revert your save from your last medbay save and you'll get to redo everything since your last medbay save.

I think iv'e screwed this up by killing celeste before going to meet him at his hideout

Just FYI: The set you give Warren does not count for the 20 gear sets achievement. You need to own 20 sets at the same time, not just craft 20.

i believe i blew this quest somehow by screwing up the JCPD outcome. i went back through multiple times throughout the game and killed everyone in the detention center. now when it's time to go see Warren for the final goodbye i go back and there is no Fletcher, no nano-monster, no console to activate, and no Repeller Coil. it's not in my Quest Item inventory so i know i didn't just get it and forget about it.
i actually don't remember Warren ever contacting me and asking me to get it for him and it is not a quest option, just "Go see Warren in the train station".

either a bug, something i did wrong through the game, or just an option that i missed somewhere and/or forgot about.

If you make the mistake of asking him any other question and loose the option to give him the repeller coil, you can exit the game ( main menu, title screen) and load back with w continue. There’s a good chance you will be loaded before talking to him and you can choose to give him the repeller coil.

I noticed a bug in atleast ps4 version. when he asks you to get the coil, go get the coil but DO NOT talk to him while he is still in his hideout. if you do, the game will remove the quest from your log and he will never call you again to get the coil (the quest will not advance) in that playthrough. you can walk by him using the shortcut but do not talk to him until the quest advances and he calls to meet you.

"Other notes on this quest: * Example * Example * Example" Ah, yes. Deepest lore. In hindsight, it all seems so obvious.