Invalid schema for gantt chart

[pdimens]

Hello, I'm trying to use vegabrite to generate visuals for genomic structural variants, which in this case are just glorified gantt charts. However, using the package, I get regular errors when attempting to do this.
The error is

Warning message:
Invalid schema for object passed to or created by modify_inner_spec.vegaspec_unit 

Here is a MWE following the gantt chart as interpreted from the VegaLite documention

df <- data.frame(task = c("a", "b", "c"), start = c(1, 3, 8), end = c(3, 8, 10))
vl_chart(height = 50, width = 700 ) %>%
  vl_add_data_frame(values = df) %>%
  vl_mark_bar(tooltip = TRUE) %>% 
  vl_encode_x('start:Q') %>%
  vl_encode_x2('end') %>% 
  vl_encode_y(field = 'task:N')

Further, a more advanced example using real data doesn't plot everything and throws the same warning/error.

> head(svfilt)
       contig population position_start position_end length type n_barcodes n_pairs     size
28 CM031716.1          1         124043       124044      1  DUP         11      32 56504578
29 CM031716.1          1         127116       290841 163725  INV         31     148 56504578
30 CM031716.1          1         145152      1048908 903756  DEL         14      32 56504578
31 CM031716.1          1         146432       442535 296103  INV         24     132 56504578
32 CM031716.1          1         146917       146918      1  DUP         27     140 56504578
33 CM031716.1          1         147886       330559 182673  DEL         76     224 56504578

vl_chart(height = 20, width = 700 ) %>%
  vl_add_data_frame(values = svfilt) %>%
  vl_mark_bar(tooltip = TRUE, fillOpacity = 0.6, height = 15) %>% 
  vl_encode_x('position_start:Q') %>%
  vl_encode_x2('position_end:Q') %>% 
  vl_encode_color(field = 'type:N') %>% 
  vl_encode_row(field = "type", type = "nominal", spacing = 0) %>% 
  vl_axis_x(grid = FALSE, domain = FALSE, tickCount = 5)

Interestingly, when I change the datatype to Ordinal, it does plot more of data:

However it forbids me from modifying the axis labels or number of ticks in an effort to hack it. In addition, it doesn't let me set an arbitrary range for the X axis to be the length of the chromosome (the size column in svfilt).

Is this a bug or user error? I am grateful for any wisdom or insight you can provide, thank you.