"Unresolved tension" refers to a situation where there is an ongoing problem or disagreement that has not been resolved or settled yet. It indicates a state of unease or conflict that remains unresolved. Full definition
(4) I am quite prepared to confess unresolved tensions in the methodological mix of history and piety. (religion-online.org)
Changes in Downing Street are rebalancing the policy playing field back towards the Tories - but leaving unresolved tensions as 2015 approaches. (politics.co.uk)
On Monday, Seoul sent jets after Chinese warplanes that entered disputed airspace, in a sign of unresolved tensions just days after the two countries met to reset troubled relations. (fortune.com)