Looking with more details I found this:
For TASK 1, the recurrence rule is RRULE:FREQ=YEARLY;INTERVAL=5;BYMONTHDAY=5;BYMONTH=10
This means that the event repeats in October 5th every 5 years (INTERVAL=5).
There's a bug
when marked as completed the first time, that's why it jumps from 2013 (the original end date is 2013-10-05) to 2018.
But I see something strange in the alarm, because it shows for last time 2018-09-30 (but I don't know why) and marked as completed on 2020-10-05. 2020 isn't related to the dates or intervals. Finally, 2018 + 5 = 2023.
TASK 3 is similar. The last alarm is set on 2015 and marked as completed on 2017. Because the interval is 1 year, it shows 2018 as next date.
TASK 2, even showing the right time, still has issues with the last alarm time.
You will need to wait until one of next (beta) builds fix this issue.
Note: this is caused only by the alarms. If you remove it, everything would work fine. Of course, this isn't a solution, but helps to isolate the problem.