This sounds like an issue I reported a long time ago against 32 bit Linux. The problem was worse on single core CPU but was still too high on multi-core CPUs. Unfortunately, I couldn’t work around the problem.
I’ve just checked Feedback and I cannot seem to find the case I logged (i’m sure Feedback isn’t listing all cases).
I did find this one from several years ago relating to MS-Windows so I guess there are some general gremlins with how sleep has been implemented.
<https://xojo.com/issue/30159>