Building using a apu was an unfortunate choice if you planned on any upgrades.
You buy a APU for the excellent integrated graphics.
But, there are no real good upgrades, particularly for a gamer.
If you install a superior discrete graphics card, you will have thrown away the big advantage of the APU.
Then, you are left with a relatively weak cpu. Most games depend on only a few fast cores.
The possible upgrades are to more cores, but few games will use more than 2-3 cores so 6+ cores are not very helpful.
Bottom line.....
What you get with a APU is what you will live with forever.
You have two issues.
1. Why the game crashes under heavier load.
If the game is fully patched and you have the latest graphics drivers, the card could be defective.
If your psu is not a good one and can not deliver the 300w or so required, that could explain your crashes.
2. Your game is cpu intensive, and largely single threaded.
Your apu has a single thread passmark rating of 1376. None of the amd processors, including the FX8 processors get more than 1500 or so.
By comparison the Intel skylake i3-6100 has a single thread rating of 2102.
You would require a lga1151 motherboard and ddr4 ram to convert to Intel.