Update:
Yesterday I tried to integrate another item in Alexa Smart Home.
As before, the new item was not found and I got the same log errors again.
After more intensive testing, I find out that apparently too many items are present through the REST API. (Yes I have many items over 500), so either the Skill runs into a time out(?).
Then I removed all the item files that were not tagged (then maybe there were 100-150 items left) and behold the new item was found.
