The following causes a infinite loop with Tcl 8.6.4 and TLS 1.6.4 on Windows and quite likely other platforms as well.

% package require tls
1.6.4
% set so [tls::socket 443]
sock00000000046A0D10
% puts $so "GET /" ; flush $so

To reproduce, you must use the above address or one where tls negotiation fails.