epoch is provided in incorrect format (and possibly incorrect scale).

[braingram]

get_catalog take an epoch argument:

stcal/src/stcal/tweakreg/astrometric_utils.py

Lines 158 to 160 in 2e422a4

	epoch : float, optional
	Reference epoch used to update the coordinates for proper motion
	(in decimal year). Default: 2016.0

However from offline conversation with Brian McLean the format should be julian year not decimal year. It is unclear if the scale should be utc or tcb.