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tl;dr: Your leddar_distance_cm_1 should be std::vector<uint8_t> leddar_distance_cm_1;

Your current code is taking the address of a temporary object (msg->distance[0]) and storing it in a pointer ( leddar_distance_cm_1) after that object goes out of scope and is destroyed at the end of the callback.

After the callback is done, leddar_distance_cm_1 is now pointing to unused memory, and the operating system is free to re-use that memory for whatever it wants. You are getting VERY LUCKY that it chooses to re-use that memory for the next message.

Instead of taking the address of the lidar data, your callback needs to copy it out of the message before that message is destructed. You could do this by hand with a for loop, but since the data is already stored in a std::vector<uint8_t>, just copying the data into another std::vector<uint8_t> will do all the hard work for you.