UDP transport in the Linux kernel

Fellow community, I need help with UDP transport in the Linux kernel.
I have an application that transmits a stream of UDP packets, which is directly connected to the receiver. The speed rate is 135 MByte per second and source and sink are single-threaded.
If I start receiver and then sender, all works as it should. However, if I go about this the other way, the receiver receives packets out of order, some it does not get at all. This lasts for several minutes on practically all frames but stabilises later on. Current receiver is simple (loop over recvfrom() ). If I inspect the process through Wireshark, everything seems to be in order.
What should I look for and what might cause the disturbance in packets when starting the process from the sender?

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