[A5120-SI] "applying QoS gives "lack of resources"

[MichaelM55]

I´m using the 5120-SI, Software Version 5.20 Release 1505P07, for access. I have to admit, I do have several features enabled, e.g. QoS settings:

traffic classifier signaling operator and
 if-match customer-dot1p 3
 if-match customer-vlan-id 10
traffic classifier payload operator and
 if-match customer-dot1p 5
 if-match customer-vlan-id 10
traffic classifier data operator or
 if-match customer-vlan-id 1 to 9
 if-match customer-vlan-id 11 to 4094
#
traffic behavior signaling
 remark dscp af31
 remark dot1p 3
traffic behavior signa
traffic behavior payload
 remark dscp ef
 remark dot1p 5
traffic behavior data
 remark dscp default
 remark dot1p 1
#
qos policy VoIP
 classifier signaling behavior signaling
 classifier data behavior data
 classifier payload behavior payload
#
qos map-table dot1p-lp
 import 0 export 1
 import 3 export 6
 import 5 export 4

One of my typical access ports looks like:

interface GigabitEthernet1/0/1
 port link-type hybrid
 undo port hybrid vlan 1
 port hybrid vlan 10 tagged
 port hybrid vlan 20 untagged
 port hybrid pvid vlan 20
 loopback-detection enable
 loopback-detection control enable
 loopback-detection per-vlan enable
 broadcast-suppression pps 3000
 qos apply policy VoIP inbound
 packet-filter 3001 inbound

When applying "qos apply policy VoIP inbound" or "packet-filter 30 inbound" to the ports, the first ports got it. But suddenly I receive errors, when adding additional ones. Either

[GigabitEthernet1/0/6] packet-filter 30 inbound
PFLT/5/FLT_SET_POLICY_RESOURCE_FAIL: Failed to apply the filter policy to or refresh the filter policy 30 on interface GigabitEthernet1/0/6 due to lack of resources.face GigabitEthernet 1/0/6

or

QOS/4/QOS_POLICY_APPLYIF_FAIL: Applying or refreshing QoS policy VoIP to interface GigabitEthernet1/0/20 failed.
Reason: Not enough hardware resource.

After deleting "qos apply policy VoIP inbound"on some ports I can actually add some "packet-filter 30 inbound" afterwards. So it seems I reached a kind of software/hardware  limit?