Let $M$ be an algebraic family of isocrystals over a base scheme $R/\mathbb{Q}_p$ (**not** a rigid analytic space).

The question is: is the set of weakly admissible points (i.e., the points $r\in R$ over which $M$ is weakly admissible) Zariski closed or open (or neither)?

The answer might be very simple and/or well-known, but I haven't been able to figure it out.

Thanks for any help!