It takes time to develop engines and test their reliability
Except the M-507 is an existing Soviet era design with 2* 56 cylinder M-504 linked together.
The problem is Zvezda were producing single digit numbers of M-504 per year in the post-Soviet era, suddenly got an order for 18*3*2 = 108 M-504 engines (6048 cylinders) ASAP.
The Management made apparently unsustainable (possibly outright fraudulent) claims about their ability to scale-up production.
On top of that (& partially excusing) they've been in parallel developing an entirely new ship gearbox manufacturing facility and design/building gearboxes and test-stands for a whole slew of ships.
Not just ships but Naval ships expected to do ASW work -> be significantly more quiet than normal ship gearboxes.
Has been big concern that a lot of institutional knowledge has been tied up in very senior & even post-retirement staff.
Recent post at Balancer forum indicates several of those have recently quit