Boundary conditions (?) in MethodOfLines.jl PDE

It’s been a while since I looked at this; as I never really got my head around this, in the meantime, you could try a simple discretization approach, so this isn’t a blocker. See Help with speeding up large ODE system from ModelingToolkit - Specific Domains / Modelling & Simulations - Julia Programming Language (julialang.org), although the simplification takes quite a while.