From 1981-08-31, CYEG:
Unparsed groups in body 'POB000' while processing 'CYEG 310100Z AUTO 00000KT 3SM POB000 BKN034 10/05 A2993 RMK SLP154 T01000050 IEM_DS3505'

POB, insofar as I can tell, means "Persons on Board," but I can't understand why that would be in a METAR?

For reference, among the tiny sliver of METARs I've looked at, the issue is also seen on:
1981-11-15 CYEG
1989-08-31
1990-11-11
1993-11-07
1995-11-05
1993-08-06 CYHM
1994-07-14
1994-07-28
1995-07-25
1995-07-28
1995-08-20
1980-06-18 CYOW
1980-07-08
1980-07-29
1980-08-05
1981-09-04
1980-09-03
1983-06-16
1983-10-29
1984-06-06
1986-06-27
1986-07-24
1986-08-15
1986-10-13
1986-11-01
1987-06-26
1988-08-02
1988-10-22
1981-08-09 CYQR
1982-07-30
1983-07-29
1990-10-28
1991-10-27
1994-06-29
1980-06-25 CYUL
1980-08-26
1980-09-21
1982-08-27
1983-09-17
1986-08-07
1984-06-21 CYWG
1986-11-02
1988-11-13
1989-08-02
1990-08-08
1993-11-21
1994-09-23
1982-06-29
1985-10-25 CYYC
1988-09-05
1992-11-08
1982-09-26 CYYZ
1983-08-26
1983-10-23
1983-11-20
1984-07-22
1984-10-14
1984-10-27
1984-11-11
1986-08-08
1987-10-16
1988-07-28
1988-11-20
1988-06-26
1995-07-15 KBHM