Wifi will not log into 2.4 ghz, but fine at 5 ghz

I have a Galaxy S3 SCH-R530C running ever 4.4.2. Everything was working fine until about a week ago when suddenly I couldn’t connect any more. Just out of curiosity, I tried the 5ghz band on my router and it connected right up. Back to 2.4 and it took a bit but connected again. I walked 10 steps from my router and bam, saved but won’t connect. Anyone run into this problem before? I’d change out the wifi module, but obviously it’s working or it wouldn’t connect at all, and the antenna is fine. Any idea’s?