My Kryonaut did the same and the temps on the GPU raised about 1-2°C after 1-2months and then stayed stable.
Noctua NH1 was little better initially for me, but after 3 weeks the temps raised 4-5°C and in the end the Kryonaut was better long term.
Also GPU's can heat up more with certain games then others, so make sure it's not that. I use Heaven Benchmark to benchmark my GPU since it a good reference to compare temps after a while.
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