Nonrecurring events aren't shown anymore - Error input string 2 FREQ

Checklist

[X] I can reproduce the bug with the latest version given here.
[X] I made sure that there are no existing issues - open or closed - to which I could contribute my information.
[X] I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
[X] I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
[X] I have taken the time to fill in all the required details. I understand that the bug report will be dismissed otherwise.
[X] This issue contains only one bug.
[X] I have read and understood the contribution guidelines.

Affected app version

1.0.3

Affected Android/Custom ROM version

Android 11 / LineageOS 18.1 20220821 instantnoodlep

Affected device model

OnePlus 8 Pro

How did you install the app?

F-Droid / IzzyOnDroid

Steps to reproduce the bug

Have a DAViCal service running
Fill the calender with recurring and nonrecurring events via Thunderbird
Connect to DAViCal with DAVx⁵
Use the calendar in Fossify Calendar

Expected behavior

Recurring and nonrecurring events should be shown and no error should be reported.

Actual behavior

Until recently, recurring and nonrecurring events were shown, reminders appeared as notifications, etc. All worked fine.

Now, when the calendar in the app is refreshed, only recurring events are shown and the following error is reported:

Error: java.lang.NumberFormatException:
For input string: " 2
FREQ"

I know I did not add any new recurring events, so I assume the error is caused by a nonrecurring event. Nevertheless, it could also originate from a recurring event, but I doubt that.

I have another device that still runs https://github.com/SimpleMobileTools/Simple-Calendar and here the recurring and nonrecurring events and notifications are working.

Screenshots/Screen recordings

Additional information

Since the calendar is working fine in Thunderbird and in Etar, this issue is very specific.

I have exported the DAViCal to an ICS file and validated it with https://icalendar.org/validator.html which doesn't report any errors.

(To export to an ICS file, log in on https://HOSTNAME/davical/ and then go to https://HOSTNAME/davical/caldav.php/USERNAME/home )

I also don't see anything wrong with:

$ grep FREQ  home.ics |sort|uniq -c|sort -nr
     14 RRULE:FREQ=MONTHLY
     12 RRULE:FREQ=MONTHLY;INTERVAL=3;BYMONTHDAY=2
      7 RRULE:FREQ=YEARLY
      4 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
      4 RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
      3 RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
      3 RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
      2 RRULE:FREQ=YEARLY;WKST=MO
      1 RRULE:FREQ=YEARLY;WKST=SU
      1 RRULE:FREQ=YEARLY;WKST=MO;UNTIL=20221221T085959Z
      1 RRULE:FREQ=WEEKLY;UNTIL=20190312T090000Z
      1 RRULE:FREQ=WEEKLY;UNTIL=20161207T160000Z
      1 RRULE:FREQ=WEEKLY;UNTIL=20161205T160000Z
      1 RRULE:FREQ=MONTHLY;INTERVAL=3;BYMONTHDAY=15
      1 RRULE:FREQ=MONTHLY;INTERVAL=2;BYMONTHDAY=23
      1 RRULE:FREQ=DAILY;INTERVAL=20

In order to pin down the problem, I would like to request the following:

For this error, please report more context, e.g. the SUMMARY and DTSTART of the event causing it. Preferably also CREATED and LAST-MODIFIED.
When the error occurs, please try to continue processing the rest of the events. If the same error occurs more than three times, stop reporting the error in a popup as it might flood the screen/CPU.
Allow to easily export a log file from the app with all errors.

FossifyOrg / Calendar