Error in upgradeUnit.default(x) : Not a unit object

[choiceMaster-ai]

Hi. I have suddenly received the error: Error in upgradeUnit.default(x) : Not a unit object executing a ggplot when I use:
...
theme(
plot.title.position = "plot",
plot.title = ggtext::element_textbox_simple(
size = 12,
hjust = 0.5,
lineheight = 1,
padding = margin(5.5, 5.5, 5.5, 5.5),
margin = margin(0, 0, 5.5, 0),
fill = "cornsilk"
)) +
...

ggplot2 version is 3.3.6
ggtext version is 0.1.1
gridtext version is 0.1.4

If I comment out the above code in the plot specification then the plot works?

Thank you