CalDAV results in 500 Internal Error using Calendar App in NC 11

I’m running into a problem getting access to the calendar app in Nextcloud 11 via a Hiawatha server, and I’m hoping someone can shed some light on what might be going wrong. Already posted this question to the Hiawatha forums, only to be told that it’s not likely to be a Hiawatha problem. I’ve been using Hiawatha successfully with Nextcloud in every other way, including with WebDAV access, which works fine. My Hiawatha setup is what is recommended. Extract follows:

MinTLSversion = TLS1.0

UrlToolkit {
        ToolkitID = nextCloud
        Match ^/\.well-known/host-meta(\?(.*))? Rewrite /public.php?service=host-meta&$2
        Match ^/\.well-known/host-meta\.json(\?(.*))? Rewrite /public.php?service=host-meta-json&$2
        Match ^/\.well-known/carddav Rewrite /remote.php/dav/
        Match ^/\.well-known/caldav Rewrite /remote.php/dav/
        Match ^/remote/([^?]*)(\?.*)? Rewrite /remote.php$2
        Match ^/index.php/([^?]*)(\?.*)? Rewrite /index.php$2
        Match ^/.well-known/acme-challenge/.* Return

VirtualHost {
        Hostname =
        EnforceFirstHostname = yes
        RequiredBinding = BaseHTTPS
        RequireTLS = yes,15768000
        WebsiteRoot = /var/www/nextcloud
        StartFile = index.html
        Alias /nextcloud:/var/www/nextcloud
        UseToolkit = nextCloud
        AccessLogfile = /var/log/hiawatha/access.log
        ErrorLogfile = /var/log/hiawatha/error.log
        TimeForCGI = 1200
        UseFastCGI = PHP7
        WebDAVapp = yes
        EnablePathInfo = yes
        AllowDotFiles = yes
        ShowIndex = no
        FollowSymlinks = yes

Both Nextcloud and the calendar app are installed at the latest versions (11.0.2 and 1.5.2, respectively, if I recall correctly). When I try to create a CalDAV connection from an iPhone, it comes back with a “cannot connect” error.

The Hiawatha logs show as follows. From Hiawatha’s access.log:

xxx.xx.x.22 - - [19/Apr/2017:11:38:43 +0100] "PROPFIND /.well-known/caldav HTTP/1.1" 500 1461
xxx.xx.x.22 - - [19/Apr/2017:11:38:43 +0100] "PROPFIND / HTTP/1.1" 405 1086
xxx.xx.x.22 - - [19/Apr/2017:11:38:43 +0100] "PROPFIND /principals/ HTTP/1.1" 405 1108
xxx.xx.x.22 - - [19/Apr/2017:11:38:43 +0100] "PROPFIND /calendar/dav/emmanuel/user/ HTTP/1.1" 405 1108

From Hiawatha’s error.log:

xxx.xx.x.22|Wed 19 Apr 2017 11:38:43 +0100|/var/www/nextcloud/remote.php|CGI returned 500 Internal Error

When I check using a web browser, URLs like the following appear to return proper sabre/dav responses:

But I get an “app not installed” response if from a web browser I try:

SSL is self-signed.

I’m stumped as to what may be going wrong. Any ideas / pointers are welcome.

I am running with the same issue, did you manage to fix it ? Thanks