The hold up is still unknown, it could be a handful of things; term, AAV, price. Morgan Frost is likely looking for a longer-term contract at 4-to-5 years but the Flyers are probably trying to get him to sign a bridge deal at 2 years.
In July, it was reported by Brandon J. Sommermann, that both parties were far from an agreement on a contract extension, meaning that talks could go into late August.
It is currently middle of August, with still no word on a new contract other than last month. This shouldn't be worrying but if things continue to head in this direction, it may be a different story.