Looks like both speed & stack size config don't apply correctly, probably a mod conflict, here's a save with a quick showcase in the sandbox, they also stop working even if you unresearch/re-research them and save/load.

https://www.mediafire.com/file/vr17iq3gsi9bg9j/Test.zip/file

is it fixed for you with recent updates?

I think so, they got their speed back, not sure about the stack size of deliveries but i have enough drones for it to not be an issue anyway.

Nvm it's still ain't applying, only speed level up to 4 works, both stack (any level, weirdly) and infinite speed aren't working (Seem like I was stuck at 60% despite being lvl 13).

I took a look at transport_technologies.lua and I think there's some issue with the infinite tech calculation? technology.level behaves weirdly from my limited testing (It seems to be off by 1 for infinite techs?), maybe a full recompute on research_finished with data directly derived from force.technologies may fix it, not sure if pairs iteration & the substring matching is an issue too since pairs iteration isn't deterministic.

I'm not too knowledgeable about factorio modding specificity tho, also really bad at reading other people's code but I think there's something in there randomly messing with the technologies (´･ω･`)?

Might be up to something, let me know if it's better with 2.0.64?

Sadly it didn't, (probably cause I have bad values cached in my save?)

I fiddled with the code a bit and managed to fix it(?), not sure if the logic is correct, but the results seems to be. I'm now sitting at the correct value (1.95) for speed at lvl 13 and the stack capacity works correctly after manually triggering refresh_all_technologies (which should trigger itself when the mod update if I understand correctly), here's the code, with a few confusing comments...

https://gist.github.com/FallenStar08/e0dd88cd2121faf38901d1f5313fcba4

Sorry for taking your time over this small issue, really liking the mod, I Like doing something other than trains for once.