The first time a terminal buffer is created, the window normal is not set as shown below. I narrowed it down to this snippet in switch_buf. The call to jobstart in convert_buf2term seems to overwrite the winhl set earlier, but setting it again right after (commented out) fixes the issue. This only happens the first time a terminal is opened, but the fix seems simple enough.
if vim.bo[buf].buftype ~= "terminal" then
M.convert_buf2term(details[1].cmd)
-- vim.wo[state.win].winhl = "Normal:exdarkbg,floatBorder:exdarkborder"

The first time a terminal buffer is created, the window normal is not set as shown below. I narrowed it down to this snippet in
switch_buf. The call tojobstartinconvert_buf2termseems to overwrite thewinhlset earlier, but setting it again right after (commented out) fixes the issue. This only happens the first time a terminal is opened, but the fix seems simple enough.