Altair/Vega Chart from GeoDataFrame not rendering in Panel

[nels]

hi,

I have an Altair chart with GeoShape marks from a GeoDataFrame.
It renders correctly on it's own in a Jupyter notebook.
However, it fails to render when inside a Panel pane.

Simple to reproduce in a notebook:

import csv
from io import StringIO
import panel as pn
import altair as alt
from geopandas import GeoDataFrame
from shapely.geometry import box
pn.extension('vega')

some dummy data

csv_data = 'i,bid,minx,maxx,miny,maxy\n0,SR01-01,20.0,120.0,855.0,925.0\n1,SR02-02,20.0,120.0,940.0,1010.0\n2,SR03-03,140.0,240.0,940.0,1010.0\n3,SR04-04,260.0,360.0,940.0,1010.0\n4,SR05-05,380.0,480.0,940.0,1010.0\n5,SR06-06,500.0,600.0,940.0,1010.0\n6,SR07-07,620.0,720.0,940.0,1010.0\n7,SR08-08,740.0,840.0,940.0,1010.0\n8,SR09-09,860.0,960.0,940.0,1010.0\n9,SR10-10,860.0,960.0,855.0,925.0\n10,BY01-11,625.0,725.0,730.0,800.0\n11,BY01-12,745.0,845.0,730.0,800.0\n12,BY01-14,865.0,965.0,730.0,800.0\n13,BY01-16,625.0,725.0,645.0,715.0\n14,BY01-15,745.0,845.0,645.0,715.0\n15,BY02-17,745.0,845.0,520.0,590.0\n16,BY02-18,865.0,965.0,520.0,590.0\n17,BY02-21,625.0,725.0,435.0,505.0\n18,BY02-20,745.0,845.0,435.0,505.0\n19,BY02-19,865.0,965.0,435.0,505.0\n20,BY03-22,745.0,845.0,310.0,380.0\n21,BY03-23,865.0,965.0,310.0,380.0\n22,BY03-26,625.0,725.0,225.0,295.0\n23,BY03-25,745.0,845.0,225.0,295.0\n24,BY03-24,865.0,965.0,225.0,295.0\n25,BY04-27,625.0,725.0,100.0,170.0\n26,BY04-28,745.0,845.0,100.0,170.0\n27,BY04-29,865.0,965.0,100.0,170.0\n28,BY04-31,625.0,725.0,15.0,85.0\n29,BY04-30,745.0,845.0,15.0,85.0\n30,BY05-36,20.0,120.0,180.0,250.0\n31,BY05-35,20.0,120.0,95.0,165.0\n32,BY05-34,20.0,120.0,10.0,80.0\n33,BY05-33,140.0,240.0,10.0,80.0\n34,SR32-32,375.0,475.0,10.0,80.0\n'

into a GeoDataFrame

gxs = [{'bid': x['bid'], 
        'polygon': box(float(x['minx']), float(x['miny']), float(x['maxx']), float(x['maxy']))} 
       for x in csv.DictReader(StringIO(csv_data))]
gdf = GeoDataFrame(gxs)
gdf = gdf.set_geometry('polygon')

chart

bays = alt.Chart(gdf).mark_geoshape(
        fill='lightgray',
        stroke='white',
    ).properties(
        width=800,
        height=600
    ).project(type='identity', reflectY=True)
bays

renders

pn.pane.Vega(bays)
no output
JS Console:
TypeError: undefined has no properties in [main.min.js:396:2301]

pn.Row(bays)
also no output
JS Console:
TypeError: undefined has no properties in [main.min.js:396:2301]

Important
GeoShape marks render correctly when the data is not from a GeoDataFrame, for instance this example renders correctly when wrapped in a pd.Row and does not produce JS Console errors.

Environment
Firefox Developer 76
Python 3.8
Libs
altair==4.1.0
bokeh==2.0.2
geopandas==0.7.0
jupyter-client==6.1.3
notebook==6.0.3
panel==0.9.5

No error messages from Jupyter.