What is the TTL of the TXT record?
How long are you waiting before you trigger the challenge?
Your DNS may not have propagated yet.
For example If your DNS Provider was Cloud Flare the minimum TTL would be 1 Minute for non-enterprise customers, which means if you trigger the challenge before 1 minute there is a chance that DNS record may not be found.
Hint: The Certificate Authority failed to verify the DNS TXT records created by --dns-cloudflare. Ensure the above domains are hosted by this DNS provider, or try increasing --dns-cloudflare-propagation-seconds (currently 10 seconds).
Change it to 60 seconds (or 30 if you are an enterprise customer)