recurring disturbance every 21 days

hi
My son Harry is 9 years. He is on ASD and his EEG showed spikes in 2022 though there was no physical manifestation of a seizure. The neurologist put him on depakote and since then he showed cognitive improvement.
However since the past 3-4 months he is exhibiting complex stereotypies (repeated movements) every 21-24 days.
This include vocalizations and hand movements. I call these internal disturbances. The disturbance lasts between 3-5 days from onset. It peaks usually on day 3 and then subsides. When he gets this his processings slows. Harry understands that something is happening which he is unable to control or explain and it upsets him. The last disturbance happened Nov 15-19 and subsided. The current one started dec 10th and is ongoing. I expect it to subside by Thursday.
Currently he is taking 180/125 mg depakote in the morning every alternate day and 250mg at night constant.
All his blood tests are normal. I can share any parameters you want.
I will appreciate any inputs or direction on this issue. I want this episodes to stop as i feel they are regressing Harry and am worried if these episodes are causing cognitive harm.