At issue is a court decision which determined the subsidy to be illegal. The appeal was originally filed under the Obama Administration and continues under the Trump Administration (for now).
"A federal appeals court on Monday granted the Trump administration a 90-day delay on its decision to appeal a case brought by House Republicans against ObamaCare subsidies paid to insurers."
This is going to create a bit of uncertainty in the markets as insurers prepare for 2018.
"Insurers need to decide by June whether they will continue to operate in the ObamaCare exchanges, and companies will have finalized their 2018 premium requests before the end of the three-month window."
Read the full article at TheHill