FaceTime 'Unavailable' and delayed iMessage delivery on iPhone despite strong Wi-Fi connection

My partner’s iPhone is actively in use (screen on, strong Wi-Fi), yet:

• FaceTime inbound shows “Unavailable” on my end and she gets no incoming call or missed-call notification.
• iMessage to her stays in a pending state (no “Delivered” or “Not Delivered”). The moment she opens Messages, it flips to "Delivered" (and then "Read" ~10s later).

This looks like background push isn’t reaching the device until the Messages app is in foreground.

Her Device:

iPhone 13

iOS 18.6.1

Apple ID Region: PH

Notifications: All on - Immediate delivery

Low Power Mode: Off

Focus / DND: Off

Background App Refresh: On

Internet (Wi-Fi)

Wi-Fi connection: Strong

Speed Test on device: 146Mbps down, 100Mbps Up

Ping <10ms

DNS Filters / VPN: None

Provider: PLDT

Internet (Cellular - But, irrelevant; she's always on Wi-Fi)

Carrier: SMART

Reception: 3/4 bars 4G

Speed Test: ~9Mbps down 7Mbps Up

Ping ~10ms

What we’ve already ruled out:

• Focus/DND/Sleep/Driving: Off; no schedules.
• Notifications: FaceTime & Messages allowed, not muted
• Blocked/Unknown filtering: I’m not blocked; Silence Unknown Callers off; Filter Unknown Senders off.
• Send & Receive: Her phone number and primary Apple-ID email are ticked in both Messages and FaceTime.
• iMessage/FaceTime activation: Toggled off/on; both show Activated.
• Network hygiene: Airplane mode reset; device restarted; Reset Network Settings done; iOS up to date.
• Profiles/VPN: No work profile. No VPNs.
• Router basics: Rebooted; firmware current.

[Edited by Moderator]

Original Title: iMessage only “Delivers” when Messages is opened; FaceTime shows “Unavailable” with no missed-call. APNs/push not reaching device in background