Mark they dont make ryzen's that small...
Trust me ive been looking for one.
If size is a concern, your best option is an intel nuc or Intel version of that unit.
However i have the intel version of that unit and its horrible. Lenovo completely botched the design on that case, and would highly recommend you go down the HP Elitedesk / Prodesk route.
Most likely there is probably nothing wrong with your unit, its most likely throttling to hell, which is the problem i have on my Intel.
The thing throttles like hell, and it has almost no airflow in that really poor design.