They were connected via port 48 on stacks, moved them to 46 on same switch in stack and it works, move back to 48 and VLAN 100 fails again.
From Stack:
vlan 100
name "VoIP"
tagged 1/46-1/48,2/46-2/47,Trk1-Trk4,Trk7
no ip address
ip igmp
exit
interface 2/46
name "7th Floor"
exit
interface 1/46
name "1st Floor"
exit
LLDP:
2/46 | 9c b6 54 d0 ef 40 48 48 SWITCH17
1/46 | 00 14 c2 45 40 e0 24 24 Switch 10
From 2920:
vlan 100
name "VoIP"
untagged 40
tagged 1-39,41-44,48
no ip address
ip igmp
exit
LLDP:
48 | 5c b9 01 27 f3 0a 102 2/46 Stack01
From 2824:
interface 24
name "Network"
exit
vlan 100
name "VoIP"
untagged 2,6,19
no ip address
tagged 1,4,7,24
ip igmp
exit
LLDP:
24 | 5c b9 01 27 f3 0a 46 1/46 Stack01