@Brook Sorry, my bad... :( A second review of my firewall setup revealed I missed a rule blocking NTP traffic for a certain IP range. Adding this device to the NTP IP whitelist solved the problem.

@Brook Same problem with a Tapo C100, after restart I get 2020-05-19.... no time&date update. My DNS resolution seems to work accordingly: n-use1-device-api.tplinkcloud.com (3.224.48.251) and...