Hello @rbl.schwarz welcome to the Let's Encrypt community. 
That is an old version of Certbot see Certbot 2.4.0 Release
That is a very old version of Chrome; I am not sure is is supported.
Please, to the best of your abilities, update Chrome.
I know this isn't the ideal answer you would be looking for; it is the best I have to offer.
Kindly wait to see if there are more knowledgeable Let's Encrypt community volunteers willing to assist.