Generally you want to do PCR tests for the big diseases (not feather tests--although they are available)--Just putting it out there..
Could be hormones or stress...
Pet on the head and neck only
12 hours of sleep on a schedule like a toddler
no access to shadowy spaces in or around the cage (boxes, bedding, huts, drawers, clothes etc)
Make sure you teach your bird to play and talk about routines...
I say "going to the store" if I will be gone for 1-3 hours...
"going to work" if it will be 4-8...
When she goes to bed, I say, "night, love you, see you in the morning"
If she stays with my parents (which is VEEEERYYY RARE) and I leave, I say "see you tomorrow!" OR I try to explain that I will be gone-- and genuinely, it seems to help.
Helping my "too" anticipate routine has really made her less anxious--she hardly messes with her feathers these days, but she was a chronic barberer/plucker (not SUPER bad, but bad enough that her chest bled a bit) when I first got her. I also am SUPPPPPER careful about keeping our interactions non-sexual and pet on the head and neck only-- she gets 12 hours sleep nightly and if I touch under a wing etc-- it is for like 2 seconds and for husbandry/care-taking only (not petting)
I use similar vocabulary all the time..If I am going to make a sound that is loud, I say, "gonna make a loud noise!"...If I drop something unexpectedly, I say "BOOM!" in an overly enthusiastic, playful voice. This stuff works for mine...really well...It's like a kid with high anxiety