EUW I've read other people having lag spikes and opened threads about it, but got cancelled. Before patch I had occasional spikes, but after last patch I got games where I have constant yellow ping and others in which I go from green to yellow(150ms) every other second and sometime even red(250+).
Done the network test and it also gives me yellow under "match server delay" if I make tests in succession.
Shoot I wish I could help more, but that is outside the realm of my expertise. :( My best advice is to make a player support case to give them more details or engage with the wild rift twitter.