The CareTeam resource contains an invariant ctm1 which leads to false errors in schematron when the reference is a relative reference:

<sch:assert test="contains(f:member/f:reference/* @value , '/Practitioner/') or not(exists(*f:onBehalfOf))">ctm-1: CareTeam.participant.onBehalfOf can only be populated when CareTeam.participant.member is a Practitioner</sch:assert>

The problem is the leading / in the contains() function. This will fail for this fragment which is perfectly legal:

<member>
<reference value="Practitioner/p01"/>
<member>

This thing is a tooling issue in STU3 as the invariant is defined in FHIRPath. The issue has already been fixed in R4 and the build

http://hl7.org/fhir/STU3/careteam.html#invs
http://hl7.org/fhir/STU3/careteam.sch