Steps to Reproduce:

1. Create a document with multiple sections one of which has a {{col-begin}} with no corresponding {{col-end}}.
2. Look at the document on a mobile device.

Actual result: In collapsed view, no sections are visible beyond the section with the missing {{col-end}}. If that section is expanded, all the later sections are visible, but they can't be collapsed or expanded individually.

Expected Result:
Document displays an error message that {{col-end}} is missing, OR this error is handled somehow, e.g., by automatically ending the multi-column table at the end of the section.

For an example of this see https://en.m.wikipedia.org/wiki/User:Danbloch/sandbox3