I used the time cheat and I put the date on March 21st. After that I sent my dwellers to the wasteland in normal time but they only collected 500 caps and nothing else, but they also took damage and used most of their stimpacks. Why did they not collect any items?
Cheating screws up dwellers in the game. They may have tried patching the cheats and causes penalties related to messing with the game's clock.
It is entirely possible that cheating has been patched and you are reaping the fruits of your labor. There are currently no new information regarding the latest patch due to Fallout 4 occupying everyone's time.
The wasteland exploration is "simulated" either if you are playing or when you launch the game. This means that if you turn your phone off after sending the dweller off, he won't do anything while the phone is off, once you start the game, it will quickly simulate how ever many hours you were away. Time-glitching doesn't stack with wasteland exploration. What you do is send the dweller off, time glitch (but obviously not 6 months or whatever ....) then recall the dweller. WAIT for the dweller to return, and finish any SPECIAL upgrades you have started, THEN return to our time. Because if you start the special upgrades and don't recall your dweller you will have something like this:
Today dweller sent to explore. Time glitch till 22nd march. Dweller knows he's been exploring for 2 months. Return to today. Recall the dweller. He'll be back on the 22nd of April
You can time glitch the resources, and they break in the same manner, but you can rush them and they fix their times. Also never use time glitch and radio (or what ever it was called) because once you are finished you get all the raiders and death claws you called, come to your door almost all together ....
Sometimes, when dwellers are sent out into the waste, they come back without items. When I sent my first dweller into the waste, they came back with nothing, after a few hours of searching. The next day, however, they had collected an Item. The longer you wait, the more likely an item is to show up. You can also try sending someone with a higher S.P.E.C.I.A.L out into the waste, as they have a greater potential, and are less likely to die.