If it's not much work to share? I'm happy to hear about it. Maybe it helps me to understand better what's exactly failing.
Even if I can work around these issues, I would like to know what is/was going on, and I'd like to provide feedback to the compiler developers. Though I also have to admit that once the type signatures get too complicated, it's difficult for me to understand what's happening. 
Meanwhile I deal with four lifetimes in my code: 'a as a lifetime argument which helps me to accept closures that aren't static (but live as long as my virtual machine), 'b as a lifetime argument that indicates how long the virtual machine is living at least (which I need for internal references), 'c as a lifetime argument when I create temporary datums from borrowed values (to avoid extra memcpy), and 'd for HRTBs, hence I end up with stuff like:
for<'c, 'd> &'d <M as Machine<'a>>::Datum<'b, 'c>: TryInto<&'d str, Error = MachineError>
And this doesn't even cover the case yet, where MachineError is replaced by a generic type, as discussed in: Problem with HRTBs and associated type bounds.
So the overall complexity (in addition to the compiler errors I encountered) makes it difficult sometimes to maintain an overview…