Hello,
@PhilippeVaucher, it's hard to determine the source of the issue, because, from the logs and the packet trace, it seems like the camera had some difficulties establishing a connection even on v7.3 of RutOS.
However, one difference that I can see, is that packets with MTU size over 1500 are being sent, which can cause all sorts of issues on LTE. To troubleshoot the issue, please navigate to Network → Interfaces → General, edit the mobile interface (mob1s1a1/mob1s2a1), and in the advanced settings, change the Override MTU option to 1200. If the connection establishes, try increasing it to 1300, 1400, 1450.
Let me know if this helps.
Best regards,
DaumantasG