The reason why LO crashes in web view could either be
- a bug in LibreOffice;
- an irregularity/issue in your specific document.
If you can consistently reproduce the issue, we look at 1. Then, it is worthwhile to solve an issue with the LO developpers. Perhaps, an issue has been filed already and the developpers are working on it. Mentioning your precise Ubuntu version and version of LibreOffice will be important, because issues like this may specifically depend on this.
If there is only a single document with which you see this happening, then suspect 2. That still may reflect a bug, but then dependent on a particular feature of the document. What can help, then, is to create a new document, copy the content of the old document in the new and continue using the new document. If the issue still happens, then you could delete sections of the document, a try to reproduce the bug each time. That will allow you to determine what section of the document may cause the problem. It may not be easy, though, to pinpoint the specific issue in that section.
If you depend critically on web view, and you are not in the ability or do not wish to use a different version - either installed from the LO PPA, or using snap, then you will need to remember to return to normal view when closing the document. To quickly resolve the issue if you forget that, you could bind the command that deletes the registrymodifications.xcufile to a shortcut key for quick recovery.
