I want to make a move to the Lede firmware from Chaos Calmer 15.05.1. However, UPnP simply does not work. The only firmware found on the official OpenWRT Wiki page https://wiki.openwrt.org/toh/linksys/wrt1900ac for the WRT1900AC that has working UPnP is Chaos Calmer 15.05.1 (kernel 3.18.23).
UPnP is working ok for me in LEDE stable and development, just in case you're on one of the development builds, check to see if Start UPnP and NAT PMP service is checked under Services>UPnP>General Settings, I've noticed in the latest builds it's not enabled by default like it was in earlier builds so it's easy to miss.
The device I'm trying to get UPnP working on is the Sony PlayStation 3. To test the functionality of the UPnP I run the ‘test Internet connection’ and after an IP address is obtained and the PlayStation Network connection has established the UPnP is checked. When it works, such as my current Chaos Calmer firmware it displays 'available’ on the test results straight away, and the table found on LuCI under Services > UPnP shows the port opened and the device it's assigned to. When it doesn't work it takes several seconds and eventually displays 'not available’ on the PS3 test results with the LuCI UPnP showing a blank table.
I did read somewhere about a newer protocol was used something along the lines of IDG2, and that older devices don't use it. The forum post then digressed onto compiling your own, older IDG1 to overwrite the newer version.