Dembélé and Griezmann were largely financed by Neymar. Their issues start around Guardiola's last year, Barcelona were alreay paying large wages to their starters and had a policy of few top level contracts and lots of youth and Barcelona B players completing the team but around 2011-2012, they started to distance themselves from that and added more and more expensive squad players. A team that already had Thiago, Busquets, Xavi and Iniesta added an expensive Fabregas, they replaced a cheap Bojan with Alexis Sanchez. The following season they added to their already expensive team, Neymar on a crazy deal that led Rossell to prison, they then got Bojan back for more than they received(he was later sold for a loss). A few years later they bring Suarez, Rakitic and Ter Stegen, now these players are very good but they came with Mathieu, Vermaelen and Bravo, all of these players had big contracts and half of them were not useful and simply cost Barcelona money. The following season they brought Turan and Aleix Vidal both useless and both costing big in wages, the following season was even worse in terms of transfers Umtiti was the only good player but his injuries ultimately turned him into a financial blackhole, the other players were Andre Gomes, Alcacer, Digne and Cillesen.
And that trend just continues, they keep spending where they shouldn't, give contracts that are unmovable, they owe departing players money and keep adding to their expenses. The issue for Barcelona is a decade of reckless behavior. The Neymar buy out was a blessing for them but they decided to keep doing what put them in a hole instead of resetting their finances.