ISML files intermittently freeze or have a long delay using VIM

[micahlunt]

Describe the bug
Intermittently when using VIM on ISML files I get the following error:
Error running task. Failed to handle key=<BS>. TextEditor(vs.editor.ICodeEditor:1,$model9) has been disposed.

Prior to the error, the keyboard becomes unresponsive. If I wait a bit, the characters typed begin to register but with a very long delay from when I initially typed. Disabling/Enabling the extension seems to fix the error for a bit.

To Reproduce
I haven't found steps to replicate that are consistent though it seems to be tied to ISML files.

Expected behavior
Keyboard input should also result in consistent and immediate results on the monitor.

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:
• VSCode version: 1.9.0
• OS: macOS Mojave 10.14.6