@t3685 Yes I'm sure.

I just wanted to tack a me-too on here. I've been converting a QTcpServer app over to 64-bit and it immediately stopped receiving signal. Connecting a 64-bit client to a 32-bit server still worked, so the problem had to be in the 64-bit server or one of the dependencies. As it turned out, the incomingConnection() had an int argument instead of a qintptr, a change we missed when upgrading to Qt5.

OK. Solution was so simple. I am on windows and there is file named hosts on the path C:\Windows\System32\drivers\etc. just edit this file and add this line:

127.0.0.1 localhost

Sometimes some application during the installation edits this file and replaces
127.0.0.1 localhost
with 0.0.0.0 localhost

so you need to fix it manually.

I suggest to use the readyRead() signal to be notified when some data arrive on the socket