Need to check the fuel line pressure with a gage. And, do a fuel pressure leakdown test.
A weak fuel pump or leaky fuel injectors or a bad fuel pressure regulator can all cause problems.
If the fuel system checks ok then test the ignition system.
Look for vacuum leaks. Make sure the EVAP system works ok. Have you ever 'topped up', if so you will have an EVAP problem.
A lot of this requires special tools and the knowledge to use them properly.
Presumeably you do not have any check engine codes stored.
Did something happen just before the problems started? Like buy bad gas? Use additives? Do a tuneup?
Check the engine compartment for rodent damage, as in chewed wires or hoses. Is there a nest in the engine air filter box?
Find a local car repair place that has 'ole school' mechanics that actuall know what they are doing and won't charge a lot of money like a dealership will.

 

Excuse my ignorance, not sure what “topped up” means. Before this started happening we did have a check engine light come on and had it scanned. Was running rich, told us it could be a gas cap so replaced it and reset codes. Then this started happening. No codes or check engine light. My son also did put in some additive prior but has before with no issues.

 

Does this Thread help: https://www.subaruxvforum.com/threa...eration-issues.189273/?post_id=2231596&nested_view=1&sortby=oldest#post-2231596

 

I’ve reached out in that post and possibly leads to an update.

 

Try putting this before filling up;
Chevron Techron Complete Fuel System Cleaner, 10 oz - Walmart.com

 

I‘ll try anything rn.

 

Spark plugs?