Are you paying much attention to the 'Resistance Haven' management and made sure you have enough on supply? Go to the pavonis site where 99.9% of the forum chat is for stuff like that

When your doom meter is full, or near full, and you have run 10 or so "intel package" mission and still didn't get a facility lead (but you have tons of rookies now, because they are awesome against Mutton Elite and the like) - you have lost. The game bent you over and did something hard to your butt - and your left scratching your head wondering why you blew off 30 or so hours to have the bullsh!t rng do that to your butt.

Chronic short supplies is a common problem. One thing to watch out for is the "unknown cause" which drains your supply payoff. If you can put high ranking soldiers in as advisors in your regions, you will start catching the faceless that are siphoning off your supplies. Once they are all gone, you will at least get al lthe supplies your havens are supposed to be providing. As for intel, do missions. More missions mean more supplies and intel, so favor intel over supply in you havens. I find that at least 5 intel slots are needed to reliably have enough time to infiltrate missions with good sized squads. Another thing. Even if they have the giant walker robot, if you stick to areas with low advent prersent, like 1-2, you likely will not run into them or can circumvent them. Hope any of that helps. I don't know if it's impossible to win, but I'm playing to have fun, and getting curb stomped every mission isn't fun for me, so I'd likely restart in your shoes.