After I posted this, I ran another test:
If I set the start date to 2018-11-15 2315hrs and end date to 2018-11-15 2330hrs, the event appears entirely on 2018-11-16 on the month view.
This occurs for any event where the start time is 2301hrs or later.

Which timezone did you set in sogo.conf?

It had been set to the following:
SOGoTimeZone = "America/New_York";

It's now this:
SOGoTimeZone = "America/Edmonton";

Restarted the server and added a new event as above. The error still occurs.

This is the raw data from an event I just created within the calendar:

BEGIN:VCALENDAR
PRODID:-//Inverse inc./SOGo 4.0.4//EN
VERSION:2.0
BEGIN:VTIMEZONE
TZID:America/Edmonton
X-LIC-LOCATION:America/Edmonton
BEGIN:DAYLIGHT
TZOFFSETFROM:-0700
TZOFFSETTO:-0600
TZNAME:MDT
DTSTART:19700308T020000
RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:-0600
TZOFFSETTO:-0700
TZNAME:MST
DTSTART:19701101T020000
RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
UID:8CD-5BEB5480-19-66E90300
SUMMARY:Test
CLASS:PUBLIC
TRANSP:OPAQUE
DTSTART;TZID=America/Edmonton:20181113T154500
DTEND;TZID=America/Edmonton:20181113T164500
CREATED:20181113T224808Z
DTSTAMP:20181113T224808Z
LAST-MODIFIED:20181113T224808Z
END:VEVENT
END:VCALENDAR

I've been doing some testing on the SOGo demo site, and can confirm that this is not just an issue on my server. Switching up the user's timezone and adding an event with an end time in the last hour of the day only seems to cause issues for certain timezones.

Some timezones where this is also an issue:
America/Adak
America/Boise
America/Yellowknife
America/Inuvik
America/New_York
America/Nassau