Problem OJS-3.1.2-1 behind proxy

Hi,
I need help, ojs 3.1.2-1 work correctly without proxy but the same application behind proxy I have a problem duplicated session :

DB Error: Duplicate entry ‘vmm2ll20n6b7hubel1t83ndv7p’ for key ‘sessions_pkey’.

I’m not finding solution, thanks for your help.