Eu868 dr7/fsk

Try to upload at DR7, not working. Node is HT CubeCell AB01, gateway Mikrotik. Everything in range DR0-DR6 works fine. Node joined at DR6, changing DR after joined doesn’t affect transmission success.
At gateway tab, live data on TTN, DR7 packet from the node is marked with SFundefinedBWNaN for the Data rate and packet isn’t transferred to the application.
Interested part of the packet:
“settings”: {
“data_rate”: {
“fsk”: {
“bit_rate”: 50000
}
},
“frequency”: “868800000”,
“timestamp”: 47450363,
“time”: “2022-02-17T08:07:38.679353Z”
},
Is it up to TTN not to accept FSK at all or expects something non standard? Or is it up to Mikrotik to wrongly fill this fields?