From the GGUS ticket:

Membership expiration notice emails contain numerous duplicates, e.g.

Dear VO Administrator,

this mail is to inform you that membership in VO na62.vo.gridpp.ac.uk for the following users is ABOUT TO EXPIRE:

Cristina Lazzeroni (7) membership will expire in 4 days.
Cristina Lazzeroni (7) membership will expire in 4 days.
Cristina Lazzeroni (7) membership will expire in 4 days.
Cristina Lazzeroni (7) membership will expire in 4 days.
Cristina Lazzeroni (7) membership will expire in 4 days.
Antonino Sergi (8) membership will expire in 4 days.
Antonino Sergi (8) membership will expire in 4 days.
Antonino Sergi (8) membership will expire in 4 days.
Antonino Sergi (8) membership will expire in 4 days.
Mark Slater (9) membership will expire in 4 days.
Mark Slater (9) membership will expire in 4 days.
Mark Slater (9) membership will expire in 4 days.
Mark Slater (9) membership will expire in 4 days.
Philip Rubin (10) membership will expire in 4 days.
Philip Rubin (10) membership will expire in 4 days.
Philip Rubin (10) membership will expire in 4 days.
Philip Rubin (10) membership will expire in 4 days.

It seems there's a problem in the velocity template or in some other rendering logic that is causing the repeated entries.