Setting up a chest that requests two or more different items using the same gate will result in only the first item specified to be delivered. For example, in the picture below, redstone and redstone blocks are requested. However only redstone arrives.

I've tried with OR gates as well but with the same result. The requester block does not have this issue, as I'm using that for now.

Updated to 7.1.14 but this may apply to 7.1.13 as well.
Found if the first condition is false then the second item will be sent.
Guessing that when a robot can't perform a transfer, it doesn't skip to the next one and gets stuck on the first. Think that's the actual issue. To tie back into my example, the following would be true.

• Chest has room for both items but there is no redstone items available. Transfer stalls despite redstone blocks being available.
• Chest has no room for redstone but does have room for blocks. Transfer is done.

that isn't realy a bug, the first request is made first, a robot can fill the request so it reserves the station blocking the second request as only 1 robot can use a station at the same time

very old issue but might still be present