There are two different problems:
FLS (Local Fiber Storage).
The next Windows Functional Upgrade will allow for about 4000 slots instead of a maximum of 128 slots.
Each plugin occupies at least one slot, but there are plugins that occupy more than four slots.
The problem of Windows 10 MMCSS (Multimedia Library).
The library has been moved from user mode to kernel mode as of Windows 10. This now limits the maximum number of virtual processors. The library is currently stable under Windows 10 Version 1809 only if the CPU has a maximum of about 14 logical processors or no more than 32 threads are occupied by MMCSS.
The second problem is not solved by the new and better FLS.
Although there should be a registration patch from Steinberg, but unfortunately the solution is only available on request and not publicly.
What Cubase 10 I do not know exactly, apparently, the program now ensures that a maximum of 32 threads are opened by MMCSS.
In my opinion, this is at the expense of performance. As long as Microsoft does not increase the maximum number of threads runs Cubase 10 with the handbrake on. (Is anyone of a different opinion?) That would mean that the performance of a 20-core CPU from Cubase when using the MMCSS only as a CPU running with 14 logical cores.
The registry patch might solve the problem, but apparently there are people who can not successfully apply the patch: