It is absolutely right. I checked stability circles and analysis clearly shows the problems. But without knowing all design details it is hard to give exact recommendations. There is not one frequency problem, it is rather relatively broadband and frequencies are high enough to make it complicated to use lamp elements. RC circuits will almost for sure make things worse due to parasitics. I think that there must be solution that limits the bandwidth for at least 5 or 6 GHz, definitely not more (if I remember the stability analysis right). Layout may also contribute a lot, especially parasitic inductance in emitter or source connection. Without seeing the design it is hard to make right conclusion. Probably these details were included in file provided by the author of the question, but I was not able to open it and check.