Environment: Mac OS 10.13.6
Acrobat Pro DC version 2019.010.20064
Build: 19.10.20064.311007

Steps:
1. Open 2 PDFs and tile them vertically
2. Activate the Comment app in both documents.
3. Collapse the Comment sidebars on both documents
4. Select some text and click on the Highlight tool in the commenting toolbar
5. Observe that both Comment sidebars expand automatically (undesirable behavior).
6. Type Command+W to close PDFs without saving.

Result:
Acrobat crashes.

Expected:
Documents both close without a crash.