[ingo] ingo - sieve error and empty filter page.

[aquilinux]

hi list, i configured ingo5 to talk with sieve, so i set up files
- hooks.local.php
- backends.local.php
- prefs.local.php

as this guide:
https://skrilnetz.net/server-side-mail-filtering-with-horde-ingo-and-sieve/
i came from horde4 where ingo/managesieve filters worked.
now i'm facing an empty filter page, with no buttons to create and manage
filters.
the log shows:

Nov  3 13:38:55 ne255 HORDE: [ingo] PHP ERROR: array_keys() expects
parameter 1 to be array, string given [pid 23235 on line 115 of
"/var/www/horde5/ingo/lib/Factory/Script.php"]
Nov  3 13:38:55 ne255 HORDE: [ingo] PHP ERROR: Invalid argument supplied
for foreach() [pid 23235 on line 115 of
"/var/www/horde5/ingo/lib/Factory/Script.php"]

any hint?

thanks!