Today I discovered another strange problem with OpenGL / Cairo:
If I open or create a project and I put a LSP plugin on a track the plugin uses openGL. If I only close the project without shutting down Ardour and reopen the same project, the plugin uses Cairo.
This goes for all projects. On first open → openGL, second open (or another project) → Cairo.
I only tested this with LSP because it’s the only plugin I know that can tell me what it’s using. I don’t know if this is an Ardour or a LSP problem.