A number of interesting performance ideas have been submitted by @kemo. PR #4833 optimizes Xls Reader in a number of different ways. One of those, slightly modified, is to use the protected `readFilter` property which is available to all classes which inherit from `BaseReader` (which all our supported readers do), rather than call the `getReadFilter` method to obtain it (often in a loop). That applies to all readers, not just Xls, and is such a good idea that I am fast-tracking it ahead of 4833. Gnumeric, Ods, Xls, Xlsx, and Xml will all receive small performance boosts from it. Csv already does this, so no change is needed there. Html and Slk do not appear to do any filtering; possibly work for another day.
Fix#4416. A peculiar problem indeed. PhpSpreadsheet has been considering a column to be filtered if any cell in the column is filtered and does not preserve the column width if that is the case. It should consider the column not filtered if any cell in the column is not filtered, and consider it filtered only if there are no cells to which that applies. At least, that's how I think it should work, and this change doesn't break any existing tests, and solves this issue.
oleibman