I fear your are not the only one having problems with traffic shaping on 860-L. Unfortunately it is not clear where exactly the problem lies, but it can be triggered by instantiating traffic shaping. It is not only sqm-scripts, but also qos-scripts that can trigger the router's susceptibility, not that helps you but see:
https://forum.openwrt.org/t/optimized-build-for-the-d-link-dir-860l/948
for more details...
Best Regards