VPN Server with multiple Pubblic IPs

HI
I’ve troubles with PPTP vpn connections

urrently I’ve a RB3011 which is configured as VPN concentrator

the net is configured as follow

/ip route
add !bgp-as-path !bgp-atomic-aggregate !bgp-communities !bgp-local-pref
!bgp-med !bgp-origin !bgp-prepend !check-gateway disabled=no distance=10
dst-address=0.0.0.0/0 gateway=195.231.89.65 !route-tag !routing-mark
scope=30 target-scope=10

/ip address
add address=a.b.c.94/27 comment=“Main Public Address”
interface=“Public Bridge” network=a.b.c.64
add address=a.b.c.89/27 interface=“Public Bridge” network=a.b.c.64
add address=a.b.c.91/27 interface=“Public Bridge” network=a.b.c.64
add address=a.b.c.92/27 interface=“Public Bridge” network=a.b.c.64
add address=a.b.c.93/27 interface=“Public Bridge” network=a.b.c.64

Actualy I’ve more than 50 pptp VPNs connecting successfully to a.b.c.94 address

for a new project I nedd to create 3 new vpn connecting to a.b.c.91, a.b.c.92, a.b.c.93 addresses.
Actually the VPN fails to connect to a.b.c.91 address, but if I change the same VPN Client to connecting to a.b.c.94 it connects immediately.

can someone please help me understand why I cannot have VPNs connecting to other IPs than .94 ?

Thanks