Sounds like a battery issue, when load is applied its voltage is falling rapidly, which is kicking off the shutdown cycle.

Have you thought to encrypt and segment each data frame then send them out in a random order over those multiple gateways, for decryption and reassembly at their destination? Two endpoints set up in this manner could provide significant security, since not only would each frame be encrypted, but the reassembly order would not be determinable via en-route packet sniffing.

Wow! 🤩 What a steal! Good job! 👍