Although the smaller iCalendar files appear to parse and unparse successfully, the resulting unparsed files are missing much of the calendar data. Below is BeyondCompare Text comparison of the source iCal file and the unparsed iCal file. Source is on the left.
Unable to render embedded object: File (image-2017-10-04-09-48-16-226.png) not found.
The parsed (infoset) files appear to include all of the data missing from the unparsed file.
Attached the source, infoset and unparsed files for one iCalendar file.