Keycloak custom login theme

Keycloak migration from 15 to 20

After migration my custom login theme is not working.

freemarker.core._TemplateModelException: 
An error has occurred when reading existing sub-variable
"loginAction"; see cause exception! The type of the containing 
value was: extended_hash+string
(org.keycloak.forms.login.freemarker.model.UrlBean wrapped 
into f.e.b.StringModel)

Can somebody help me out