If you are using 1,8 ghz perhaps your system is not so overclockable as others. Try reducing to 1,6 ghz or 1,4 ghz to see if it improves. I personally never got a freeze using PPSSPP or any app at 1,8 ghz. But it's not guaranteed that all devices support overclocking at 1,8 ghz or the DDR overclock. Some cpu apps have issues with overclock when applying them on boot. Perhaps you can try a different cpu app. I use setCPU.
I suppose you use the same version of PPSSPP and the same options in the game you mention, just in case it's not a issue with that particular game or something.