Team debt is a condition where team spirit and morale has been neglected for a period of time. This is a matter of priorities; for example, perhaps product development had to come first because there was a deadline to be met.
Like technical debt, team debt can accumulate only so much before being addressed. If the underlying issues are not dealt with or the situation not solved, the debt will impact the scalability of the team and its potential. The team will be fixed on old issues and unable to move on.
Team debt, however, has to be addressed urgently after that period of time due to two reasons. One - team issues are psychological and may require more deeper probing and understanding before being solved. Two - even after finding the solution, the implementation may be difficult and lengthy. Both these reasons contribute to the undefined period of time needed to address team debt, which is why urgent attention is required.