`<C-o>` delay with autocomplete popup

Describe the bug
In insert mode, pressing Ctrl-O switches to normal mode for one command, then switches back to insert mode when the command is finished. However, in VSCodeVim there seems to be a delay (cooldown, maybe?) of 1 second maximum for this keymap, which occurs when having the autocompletion popup showing up, forcing the user to press the mapping repeteadly.

To Reproduce
Steps to reproduce the behavior:

1. Type any text while in insert mode.
2. After finishing to type, quickly use the Ctrl-O keymap.
3. If the autocompletion suggestions display was present, it will unexpectedly not work, slowing down the general typing process.

This bug happens randomly even without the autocomplete window present, but it is more obvious with it.

Expected behavior
Have it instantly snap back to normal mode, regardless of state.

Screenshots
If applicable, add screenshots to help explain your problem.
If remapping-related, please attach log output: https://github.com/VSCodeVim/Vim#debugging-remappings.

Environment (please complete the following information):

• Extension (VsCodeVim) version: 1.8.0
• VSCode version: 1.33.1
• OS: Windows 10

Additional context
Add any other context about the problem here.

Start by reproducing the Ctrl-O mapping in VSCodeVim 1.8.0 while the autocomplete popup is visible, then compare behavior with and without the popup. Trace the insert-mode-to-normal-mode transition and identify where the delay or missed keypress occurs. Done means Ctrl-O switches modes immediately and reliably in both states.