Importing bigger .ICS files only imports part of it

Steps to reproduce

1. Export your old calendars
2. Reimport a big .ics file (>= 100KB) e.g. create a new calendar
3. Wait, till NC notifies about a timeout and counts down to refresh the page (here it was ~20secs)

Expected behaviour

The importer should deal with every file (size) that was also create by NC sucessfully. This is essential for user backups and user doesn't noticed, that he gets a corrupted reimport (and might start working on the calendar).

Actual behaviour

You don't see any hint about the ongoing import, but only a message that the page will be refrehed.
I managed to splitup the files till ~ 50kb to workaround this bug. This seems to be a regression and I noticed a similar problem to the contacts import.

Calendar app

Calendar app version: 2.0.4 (but same behaviour on NC 19.0 before)

CalDAV-clients used: -

Client configuration

Browser: Firefox 80

Operating system: Linux Mint 10

Server configuration

Operating system: Centos

Web server: nginx

Database: mariadb

PHP version: (e.g. 7.0.3)

Nextcloud Version: 19.0.2

Updated from an older installed version or fresh install: fresh

Start by reproducing the large-file import with the reported calendar app and Nextcloud versions, comparing a file around 50KB with one at least 100KB. Trace the calendar importer and timeout behavior to determine why the import stops early; done means the complete file imports successfully without a misleading refresh notification, with the regression and contacts-import behavior checked.