2014 Nissan Juke 1.5 dCi- starting/ stalling issue

Hi everyone, I'm hoping someone with experience with the 1.5 dCi Juke might be able to point me in the right direction because I'm getting different opinions from different mechanics.

I have a 2014 Nissan Juke diesel, around 114k miles. The problem mainly happens when the car has been sitting overnight or for a long period.

When I first start it, it fires up but runs really rough/shaky for 1–2 seconds and then stalls. Sometimes it takes multiple attempts to start. I've also noticed that if I press the accelerator when starting it, it's much more likely to stay running. Once it's running properly, it generally drives normally.

The first mechanic checked the car and couldn't find anything obvious. He did find dirt/contamination in the fuel filter, so he replaced/fixed the filter. Unfortunately, the starting problem is still there. If anything, I feel like it's become a little worse since the filter was changed.

He said the battery and glow plugs were fine, but mentioned that the injectors could be an issue and that he wasn't really able to investigate them properly.

I then spoke to another mechanic who doesn't think it's the injectors. He thinks it could be a DPF issue and said the DPF needs sorting anyway, but he couldn't guarantee that doing the DPF work would actually solve the starting/stalling problem.

I don't want to start throwing money at parts without knowing what's actually wrong.

I would appreciate any sort of guidance or help from anyone. Thanks.