Strange voltage on RST pin msp430g2553 TSSOP 20 pin

Dear everyone,

I made six pcbs, but only one pcb well-worked.

I just wrote a program to test LED and Interrupt on button with LPM4.

My problem is only one pcb has about 3.3V on RST (well-worked), another about 2.2 to 2.8V.

The lower one only work for a short time, after that it turns to be uncontrolled.

I take off the chip and measure on RST pad (with out MCU), it is 3.3V.

So I hope your help to figure out where is my failure, why the RST pin was dropped voltage, was my MCU broke?

Please give me some suggestions to solve my problem.

Thank in advance!