Hi, I'm having the exact same problem - except I'm forwarding to localhost:443 because of SSL.
When I first try to go to 127.0.0.1:8888/phpmyadmin - it says 400 Bad Request (speaking HTTP to an SSL-enabled server port)
So, instead, I try to access via https://127.0.0.1:8888/phpmyadmin - but it does not connect.
Putty event log said:
2020-04-30 12:28:11 Opening connection to localhost:443 for forwarding from 127.0.0.1:61443
2020-04-30 12:28:11 Opening connection to localhost:443 for forwarding from 127.0.0.1:61444
2020-04-30 12:28:11 Forwarded port closed
2020-04-30 12:28:27 Forwarded port closed
I'm sure the port is open on AWS, and I've tried forwarding it to a different port.
Any ideas of what else I could try?