I would think this is possibly a routing issue.
route outside 0.0.0.0 0.0.0.0 126.96.36.199 1
I can see you have NAT’d both interfaces using the relevant IP blocks from your providers, however you are routing all traffic to provider IP 188.8.131.52.
This provider may be dropping the traffic from the 184.108.40.206 as possible IP spoofing.
Just a thought.
Adding some information to the above answer.
Your default route points to ISPA so no traffic will be routed to ISPB. You might be able to configure a 2nd default route with a higher admin distance pointing at ISPB Something like this;
route outside2 0.0.0.0 0.0.0.0 78.x.x.x 10
I haven’t tried this on a pix but it should work. The effect would be all traffic would take ISPA until the interface to ISPA went down, at that time all traffic would take ISPB. You would also have to configure NAT properly for each outside interface.
If you want something more advanced, like distributing traffic load across both ISPs at the same time you’ll need to get a router and connect your ISPs to it instead of the pix.