When PRODID has exactly 75 characters, it's folded without obvious reason:
VCALENDAR
VERSION:2.0
PRODID:DAVx5/4.5.5-gplay ical4j/3.2.19 (com.simplemobiletools.calendar.pro)
BEGIN:VEVENT
This can happen for special combinations of DAVx5 version numbers and calendar app package names.
Although it may be technically valid, it's confusing and there are servers like iCloud which seem to reject such iCalendars.