I have a 16 foot pontoon and I have 2 digger anchors and it’s almost impossible for me to get them set on the lake bottom. The instructions say not to use chain with these types of anchors. I’ve tried letting a lot of line out I’ve tried using the boat to set the anchor and even in mud and sand i can’t get them to set the majority of the time. Any suggestions on how to fix this? Does anyone use these anchors? I got them bc they were considered the best for pontoons but I’m not convinced. I have a hard time getting my boat anchored from front and rear to fish where I want and keep the boat still. I do most of my fishing on Eagle mountain and lake worth and both are muddy bottom lakes.

I dont use that type. But, I have a bass tracker pro 17 and I cant anchor.,I use anchors on back and front and float all around the lake. so irritating.

Anchor up right and get the right anchor.

https://goneoutdoors.com/anchor-pontoon-boat-6113284.html

I have used a Digger on a 22 foot bay boat CC for over 20 years. Fished in up to 90 feet of water at Amistad for Catfish. As you say no chain and I use 3/8 inch anchor rope because I have an anchor retrieval system to save my fishing partners backs. The 3/8 rope works better with the pulley on the retrieval buoy (bag). I dont recall ever using a rope longer than 200 feet and have never had a problem getting the Digger to set. I did lose one at Possum Kingdom years ago because it was apparently locked up in some big trees and I couldnt get the tines to release. I just make sure to let out enough slack to keep the tines trying to dig. I have heard that BOX anchors work well on pontoons. Good luck.

The few times I’ve had it grab it locks down but I think I realized my mistake after researching a little. Gonna go see what I can do. I haven’t been letting the full scope of the line out before trying to set it

Just use a Danforth and some chain. There are aluminum Danforth anchors available if you want to save weight (I keep one in the poling skiff in case I need to ride out a storm). I've been using Danforths for over fifty years. They work extremely well in sand and mud, and fairly well in gravel.

Another problem I’m having is even if I get the front and back locked down the boat sways so much it’s impossible to keep tight lines...

We have a big tritoon and use a box anchor at Canyon Lake. Works great except in highest winds.

The problem with anchors is there's an anchor for every type of bottom known to man. https://www.westmarine.com/WestAdvisor/Selecting-The-Right-Anchor
If you were close by, I'd let you borrow my Danforth with chain and go out with you to see if that solves your problem. You may try that with someone in your area. As far as swinging, I use a Danforth on the bow and a mushroom anchor on the back.
Another couple of things to consider that are more expensive but will solve the problem, is to get a couple of powerpoles or a GPS trolling motor that you can spotlock.

When we had the pontoon, we used this one

https://www.basspro.com/shop/en/bass-pro-shops-anchor-kit-1-4-x-5-chain

and this one

https://www.basspro.com/shop/en/bass-pro-shops-mushroom-anchor

Drop the anchor, drift back, see where your swing is, drop the mushroom and tightenup.

The top anchor held my 22ft toon in winds higher than I should have been out there without issues