Bug Report? (Stop and Go, Isolated)

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1

Initial transfer of complete Sync to new device.

  • “Source”: Macbook Air M3, Sequioa 15.6. Syncthing v.1.30.0 (64-bit). Wifi connected. Established Node. Syncthing shared folder Sync to many hosts. Introducer. WQXNO3N-xxx

  • “Destination”: Mac Mini M4, Sequoia 15.6. Syncthing v.1.30.0 (64-bit). Ethernet connected. Newly erased and rebuilding. Syncthing shared folder Sync only to Macbook Air, right next to it. (All other hosts are paused.) XTKLHTB-xxx

  • Connection: Ethernet/WiFi, plus Thunderbolt between them.

  • Source of syncthing: brew.

  • Folder: ~/Sync . (No default Folder in order to avoid conflict) About 160GB, about 330,000 files. Initial Sync transfer.

Whenever I restart the connection (e.g., reboot of Macbook Air, restart of Macbook Air Syncthing, restart of Mini, etc.), about 500-1000 files are transfered nearly instantly. Then complete stop.

The log on the destination Mini (XTK…) tells me

025-08-09 09:54:55 My ID: XTKLHTB-xxx
2025-08-09 09:54:56 Hashing performance is 1752.66 MB/s
2025-08-09 09:54:56 Overall send rate is unlimited, receive rate is unlimited
2025-08-09 09:54:56 Relay listener (dynamic+https://relays.syncthing.net/endpoint) starting
2025-08-09 09:54:56 Using discovery mechanism: global discovery server https://discovery-lookup.syncthing.net/v2/?noannounce
2025-08-09 09:54:56 Using discovery mechanism: global discovery server https://discovery-announce-v4.syncthing.net/v2/?nolookup
2025-08-09 09:54:56 Using discovery mechanism: global discovery server https://discovery-announce-v6.syncthing.net/v2/?nolookup
2025-08-09 09:54:56 Using discovery mechanism: IPv4 local broadcast discovery on port 21027
2025-08-09 09:54:56 Using discovery mechanism: IPv6 local multicast discovery on address [ff12::8384]:21027
2025-08-09 09:54:56 Ready to synchronize Sync (sendreceive)
2025-08-09 09:54:56 ...
2025-08-09 09:54:56 TCP listener ([::]:22000) starting
2025-08-09 09:54:56 QUIC listener ([::]:22000) starting
2025-08-09 09:54:56 GUI and API listening on 127.0.0.1:8384
2025-08-09 09:54:56 Access the GUI via the following URL: http://127.0.0.1:8384/
2025-08-09 09:54:56 Ready to synchronize Syncwww (sendreceive)
2025-08-09 09:54:56 My name is "homepuck.socal.rr.com"
2025-08-09 09:54:56 Device JXENG6D-xxx is "xxx" at [dynamic]
2025-08-09 09:54:56 Device WQXNO3N-xxx is "air15" at [dynamic]
2025-08-09 09:54:56 Device WSWLOAI-xxx is "xxx" at [dynamic]
2025-08-09 09:54:56 Completed initial scan of sendreceive folder Syncwww
2025-08-09 09:54:56 Completed initial scan of sendreceive folder Sync
2025-08-09 09:54:56 Established secure connection to WQXNO3N at 169.254.23.122:22000-169.254.180.89:22000/tcp-client/TLS1.3-TLS_AES_128_GCM_SHA256/LAN-P10-xxx
2025-08-09 09:54:56 Device WQXNO3N client is "syncthing v1.30.0" named "air15" at 169.254.23.122:22000-169.254.180.89:22000/tcp-client/TLS1.3-TLS_AES_128_GCM_SHA256/LAN-P10-xxx
2025-08-09 09:55:15 quic://0.0.0.0:22000 detected NAT type: Full cone NAT
2025-08-09 09:55:15 quic://0.0.0.0:22000 resolved external address quic://172.249.43.52:1026 (via stun.xten.com:3478)
2025-08-09 09:55:15 Joined relay relay://104.194.77.215:22067
2025-08-09 09:55:30 Failed to acquire [::]:22000/TCP open port on NAT-PMP@192.168.1.1: getting new lease on NAT-PMP@192.168.1.1 (external port 35417 -> internal port 22000): read udp 192.168.1.29:57291->192.168.1.1:5351: recvfrom: connection refused
2025-08-09 09:55:30 Detected 1 NAT service

The log on the Macbook Air has gone silent. No new requests. Just sitting there since 09:54:56 connection to the mini logged.

Reproducible.