Without any explanation of the screenshots, all I see is that a packet with frame counter 8 is missing. This is wireless; there’s no guarantee that all transmitted packets will indeed be received. Like maybe it collided with a packet from another node. (You’re sending text, and using SF12 which is the worst, yielding an air time of more than 1.3 seconds. Hence chances for collisions with other nodes using the same SF are high too.)
If you’re saying that your node is refusing to send every 10 seconds: yes, that’s very much to be expected. When sending 4 bytes of application payload on SF12 (requiring 1.318 seconds for each packet), EU868 duty cycle limitations only allow one packet every 131.89 seconds for a 1% duty cycle. If all is well then your node’s software should indeed enforce that and refuse to send more often. But that’s by design, and certainly not referred to as “packet loss”. See https://www.thethingsnetwork.org/docs/lorawan/duty-cycle.html
Beware that even one such message every 2 minutes is way too much for TTN; instead only 22 messages per day would be within the limits. See Limitations: data rate, packet size, 30 seconds uplink and 10 messages downlink per day Fair Access Policy (which also explains: don’t send text).
Finally: I don’t know what “switch to class C done” means, but TTN only supports Class A.
(Please don’t post images for text-only content, such as the node’s log. Please re-read before posting; things like “only gets delivered” are clearly missing something, and “shows only null data” needed much more detail. And please don’t post screenshots that include the same data twice. We’re happy to help, but not too happy to need to decipher your question.)