Nokia has filed numerous patent infringement complaints against Oppo regarding SEP and non-SEP patents. These patents are about connectivity, interface and security features. The complaints are filed in European and Asian markets.
Oppo and Nokia signed a multi-year licensing agreement back in 2018 and it seems that the contract is over. Nokia put out an official statement that Oppo has rejected the offer of renewing the contract so it had to take legal actions since Oppo continues to use those patents. The spokesperson for Nokia believes that there is still a more constructive way to deal with the situation.
Nokia, after all, has quite a lot of patents up its sleeve and has signed royalty-bearing agreements with Samsung, Apple, LG, Lenovo and even Blackberry.