this isn't super helpful, but from former electronics experience i would recommend using rosn core solder. idk if that's what your using or not or if its the iron. but it looks like there's a bunch of flux on the board that can slowly corrode the pcb. using flux on the board and then putting on solid solder will work, but its not the best from my experience. again from my best experience using some of the thin rosn core solder from radio shack has worked great for me for the past 6 years working on hobby electronics.
as for your problem it could be a bridge in the connections or the gunk around the solder points. don't know what else might be a possible culprit atm.
I'll try to get my hands on some new solder.
As for the double post, CMO still doesn't support deleting posts for some reason, but most people just edit them and write "double post" or something similar.