Swab test keeps coming back positive for ketamine?

Hi, for the past 5/6 months I’ve been doing weekly drug tests as my adhd psychiatrist took me off my medication due to me getting drug induced psychosis. He said I can come back on it when I’ve passed 4 swab tests in a row. Every single test I’ve done has been sent off to a lab by my drug worker and then come back positive for ketamine. We are both really confused because these tests have a detection window of about 3 days yet I’ve barely done much ketamine since starting these tests, even been a month solidly clean and it still comes up positive? My drug worker has given me a couple of urine tests to try now which supposedly have a longer detection window and these have both come back negative but sadly my psychiatrist will only accept the swab tests. Does anyone have any theories as to why this might be happening? No other drug comes back positive, just ketamine. I have cut down almost entirely since I developed psychosis but before this period I was using ketamine a lot and for a long time, many years, although I’d been in the drug services a while and before working festivals during summer was also cutting down quite a lot. So maybe it’s due to the long term using of the drug? But it just makes no sense even my drug worker said she believes me but she’s never come across this happening before. It’s just very frustrating because I am struggling a lot being off my adhd meds and wish I could understand why this keeps happening. Thanks!