Both synchronous and asynchronous run-time parameters are fully supported in the x86 simulator. However the precise timing and cycle accuracy of when an RTP update occurs differs between the x86 simulator and the AI Engine simulator. Asynchronous RTPs in particular do not affect a kernel on a specific known cycle by their very nature of being asynchronous. This is true of asynchronous RTPs in both the x86 simulator and the AI Engine simulator.
Note: The x86 simulator by its nature is a functional level simulator whereas the AI Engine simulator models cycles (approximately). It is expected there will be differences. Xilinx recommends you consider partitioning your design into pieces that benefit from the x86 simulator.