I am in no sense of the word an experienced grower and very well could be wrong but I think your biggest problem is starting the seedlings in those jiffy pellets. I have done this a couple of times now and I know others who have done the same and each time the seedlings either die or are very stunted in growth. I use them for clones only now and they work well for that, germinated seeds now go straight into soil and haven't had the same problems since. If you peruse posts on many of these forum sites you will see many have the same issue with the jiffy pellets, unhealthy tiny plants that grow very slowly.
Jiffy pellets can be tricky but used correctly they do work fine for starting seeds. I started 72 pellet flats of various seeds (vegetables, cannabis and herbs) with them the last couple of springs and germination results were normal.
The tricky parts are:
1) Getting the initial soak to expand and hydrate them right - it’s easy to over-wet them if not careful with volume of water
2) Pellets dry out very quickly (like in one day at my house) once they are taken out of the clear humidity dome, especially if running a fan for airflow. Its pretty dry in my house in Feb-Mar when I start seeds though.
3) If the mesh nets are removed before transplanting it’s easy to disturb roots and accidentally break apart the peat when doing this.
Popping them into solo cups with soil mix 2-3 days after seeds germinate works to fix the issue with them drying out too fast.
I also found little difference between removing the nets or leaving them on but this is a big topic of debate both on vegetable gardening forums. YMMV on the nets.
I’ve had a couple of pretty successful years using them to start seeds but am not going to use them for 2022. The drying out too quickly thing is what I like least about them. Transplanting to larger containers with minimum mess is what I like most vs starting in soil.