There is a known issue that's currently being worked on. It's listed as DE19023 with the following details:
Post 8.0.x upgrade, there's an issue where the heatmap xml file is not being built due to resource contention.
The current workaround has been to increase the threads allocated in VisualRF Setup. Core threads/Location caching threads/UI threads should all be equal to the number of cores on your server. If you're not sure how many cores are present, visit System -> Performance and you can determine from the type of CPUs present:
For example, the below is 8 cores, so I'd set VisualRF to have 8 threads for all 3 settings:
CPU
Intel(R) Xeon(R) CPU X5560 @ 2.80GHz Hyper-Threaded 4 Cores 8192 KB cache (2793.283 MHz actual)
Intel(R) Xeon(R) CPU X5560 @ 2.80GHz Hyper-Threaded 4 Cores 8192 KB cache (2793.283 MHz actual)