MacVim hangs for minutes with hundreds of threads

Describe the bug
I'm a daily user of MacVim and my work depends on it. MacVim occasionally hangs for minutes with hundreds of threads (500 or more) when editing some specific large file(s). I had this happen several times, but only once a day at the most. It could be a syntax highlighting problem perhaps. It's difficult to reproduce exactly.

To Reproduce
Detailed steps to reproduce the behavior:

1. Run open -a MacVim Forth500.s
2. Edit Forth500.s and perhaps some other files in other windows (but don't think that matters)
3. Change Syntax to Assembly/Turbo then navigate, search, type, etc.
4. Eventually the problem occurs, but I can't tell when and why. It may happen after a while, so it's not frequent, fortunately for me.

Expected behavior
No hot laptop!

Screenshots
N/A

Environment (please complete the following information):

• MacVim version: Custom Version 8.2.2681 (171)
• OS: MacOS 10.15.7
• Terminal: N/A

Additional context
The Forth500.s file is here: https://github.com/Robert-van-Engelen/Forth500/blob/main/Forth500.s

まず open -a MacVim Forth500.s でハングを再現し、Assembly/Turbo 構文を使用して移動、検索、または入力を行いながら Forth500.s を編集します。提供された Forth500.s ファイルおよび報告された MacVim 8.2.2681 環境と動作を比較します。信頼できる原因を特定し、数分間続くハングとスレッド数の増加が発生しなくなったことを確認できれば完了です。