The warning does not show up there. It still samples slowly but I should note that it is running on a 24x24 covariance matrix so maybe this is to be expected? The dataset is only ~4000 rows however.
I tested it on mock data generated from my random function and it still gets the same warning and runs at the same speed.
Here is the mock model and data as well as my updated logp and random functions if anyone wants to test it.