officer pptx variable won't save with saveRDS

[JPR]

Folks

I have a working Shiny app which runs a number of long running database queries. I successfully use future_promise() to run those queries in a background process. In one of these background processes, I also give the option to generate output to a PPTX file via the officer package.

In order to pass the output of pptx <- read_pptx() between processes, I first created variable pptx as global. While this worked, it limited multi-user ability.

I've attempted to store the pptx variable in a file via saveRDS() (as well as save()), which seems to work. In the background process, I read the pptx variable back in via readRDS() (and I've tried load() as well). This also seems to work, but when I attempt to pass the now local pptx variable to an officer function, the function fails with "external pointer is not valid".

A slimmed down example of this issue would look like:

pptx <- read_pptx(path = "PreRenewal-template.pptx")
saveRDS(pptx, file="_pptx.rds")

observeEvent(
input$pptButton,
{
pr_pptx <- future_promise({
pptx <- readRDS(pptx, file="_pptx.rds")
pptx <- on_slide(pptx, index=1) # this line will fail with "external pointer is not valid"

}) %...>% 
{
      print("pptx serialized to RDS file")
} %...!% 
{
      print("pptx errored while serializing to RDS file")
}
})

Any clues as to why saveRDS/readRDS is not behaving with the pptx variable?

Thx!
Joe