First few packets after power cycle are often not sent from modem

[Bobblybook]

Using MKR1300 with 1.2.4 firmware/lib. TTN on AU915, sub-band 2. Testing with the LoraSendAndReceive example sketch (with confirmed uplinks changed to OFF).
When powering on the arduino, the first few packet transmissions are very unreliable. Even when loading in a known good dataRate, the first few packets often fail to send from the modem module at all. Sometimes they go through first try, often not.

After a number of failed packet sends, one eventually makes it through. Then there is some communication with the server via downlinks and then the packets are very reliable.
Is there any way to avoid this "warm up time"? I can save prior negotiated parameters to memory if needed, but I can't seem to prevent this failed packet sending on arduino startup.