BOOT probem

I have working with STM32L083... Since now no problem observed but my last pcb has BOOT problem... Namely when I ACTIVATE BOOT signal STM enter to boot mode but when I relesed taster for boot signal MCU resume from boot mode... earlier version of pcb after releasing taster MCU stays in boot mode and software upadting trough to USB works perfectly..... No observed pcb chaging.. ANy ideas?