An ACX configured for PTP mode under the chassis stanza:
set interfaces et-0/0/27 flexible-vlan-tagging
With PTP referencing port 0/0/27:
set protocols ptp clock-mode boundary
set protocols ptp profile-type g.8275.1.enh
set protocols ptp domain 4
set protocols ptp slave interface et-0/0/27.4094 unicast-mode transport ipv4
set protocols ptp slave interface et-0/0/27.4094 unicast-mode clock-source 10.55.249.163 local-ip-address 10.55.249.162
And, port 0/0/27 defined:
set interfaces et-0/0/27 native-vlan-id 666
set interfaces et-0/0/27 speed 1g
set interfaces et-0/0/27 mtu 9216
set interfaces et-0/0/27 unit 4094 vlan-id 4094
set interfaces et-0/0/27 unit 4094 family inet address 10.55.249.162/31
Is reporting an alarm tied to PTP and invalid port speed configuration as well as a report that PTP is not functional:
labroot@f22-37> show chassis alarms
2 alarms currently active
Alarm time Class Description
2024-09-01 06:20:30 PDT Major FPC-0 PIC-0: PTP might not be functional becasue of Invalid Port Speed Configuration
2024-09-01 06:20:30 PDT Major FPC-0 PIC-0: Invalid Port Speed Configuration, Refer 'show chassis pic'
From the documentation:
https://www.juniper.net/documentation/us/en/software/junos/interfaces-ethernet/topics/topic-map/port-speed-acx-routers.html
Or:
"If you configure Precision Time Protocol (PTP), port 27 is disabled."
So, 0/0/27 cannot be used when PTP is active. This limitation is also referenced on Pathfinder via the PortChecker application:
https://apps.juniper.net/port-checker/acx7024/