I went from global rank 30k to global rank 50k in the course of two matches, both of which I won...
There were no matches played by me in between the matches shown in the screenshots.
It's probably because you've been losing matches since you've reached the rank of 30k which causes your ELO to go down. When you fought the person with a 50k rank, your ELO was close to his so your rank went up.