If nothing is shown in the firewall log, then creating a floating rule like you proposed (https://forum.pfsense.org/index.php?topic=71515.msg414518#msg414518)wont help.. Unless you have rules that match but don't log traffic. But i think that this kind of problem is unlikely to be the cause of your current issues..

You could try is disabling the trafficshaper, maybe that 'interacts' strangely with squid..??

Would also be interesting to see some packet captures of both the wan and lan side simultaneously while a failing upload is being made, so it is clear which side of the connection 'breaks'. Then combine that with logging of squid with a higher then normal verbosity and it should help in determining what part of the process causes it to fail.

Greets PiBa-NL

-Does your 'firewall log' show any blocked traffic related to the upload?
No , in fire\wall log nothing relate to my ip
i clear the firewall log and put my ip in the source  and choose  the three option (reject blocked accept)
nothing relate to my ip

-configured the browser to use the proxy? or using transparent-proxy?
configured the browser to use the proxy

-using https with MITM-attack and a certificate configured?
no

-'everything' else works correctly? (besides the >512kb upload)

everything is pretty ok  , (download restricted by traffic shaper and work very well)

also i looked inside squidguard log for blocked item there is nothing relate to upload

by the way i use pfsense v 2.1.2 + squid3-dev

-Does your 'firewall log' show any blocked traffic related to the upload?
-configured the browser to use the proxy? or using transparent-proxy?
-using https with MITM-attack and a certificate configured?
-'everything' else works correctly? (besides the >512kb upload)

Greets PiBa-NL