A bug in Nextcloud Server 17.0.1 causes the workflow rules to depend their behaviour on the file extension when checking file mimetypes.
{
"versions": [
{
"introduced": "0"
},
{
"fixed": "15.0.14"
},
{
"introduced": "16.0.0"
},
{
"fixed": "16.0.7"
},
{
"introduced": "17.0.0"
},
{
"fixed": "17.0.2"
}
]
}