All of the above suggestions have merit.
One thing that many times racers and even engine builders do not pay a lot of attention to is the matching of components for their intended use and the surrounding cast members in the rest of the engine. Many of the roller lifters available through main stream cam companies just don't cut it for me. If it is a race engine it will get pressure fed lifters with internal oiling. Lifters are a huge weak link.
Incorrect valve springs and spring set-up are another huge wealk link that can cause all you mentioned and worse.
I hope you have not had a rocker nut adjuster back off, but if if you have you are not the first one to have this happen. Adjusting and tightening to lockdown is another thing that is often done incorrect. If done correct the nut will never get loose.
Use pushrods that have special 270 degree hardned ends pressed into them which are available only through speciality pushrod companies, like Manton, Smith Brothers, Trend, etc. I hate cam company pushrods for anything except street use.
Usually when an engine experiences strange valvetrain happenings it usually is caused from too weak of springs or too much clearance between coil bind in the setup. All of the other things previously mentined also can cause issues.
Kind of like what came first, the chicken or the egg. One thing goes wrong and causes efeects to other things that go wrong at what seems to be the same time.
Ed