Suction is weak and the tips are up instead of staying down on the floor of the pool

Air trapped in the unit. They do not float unless air is trapped. Turn upside down under water to relieve trapped air.

If return inlet fittings are STRONG with plenty of water returning, then that means water is being sucked from somewhere else in addition to your weak skimmer, Right?
So that means you must have another point of suction somewhere that is also open, especially with knowing, that suction at skimmer is weak!
To increase suction at any one point, close down other suction ports. In your case probably a second skimmer that is "tee, d" together, then in which case you will need to physically plug that openings suction port, if there isnt a valve to do so. Or your bottom main drain is open ?

I am going to presume you are a seasoned user of this style of cleaner? If not, then a common mistake that new users make, is a simple fix. Understand that water flow via suction, will take the path of "Least Resistance"! Check to see & ensure if any other port of suction is closed down, you need the 'majority' of the suction (75% or more) to be at the port where the pool-vac hose is plugged into.

Check the motor and clean it properly. A very dirt motor will cause no suction or weak suction.
Be sure the motor is running on proper speed, a weak motor will cause a weak suction.
Thanks for asking.

It's most likely a piece of debris in your flapper of your automatic pool cleaner. Debris may prevent flapper movement or restrict flow. You might also want to check for proper hose balance. The hose should stay at a 45 degree angle to the pool floor. If it is greater than a fourty five degree angle, the hose is too light. Move the weights closer to cleaner, or move the first two weights closer to each other. If it is less than a 45 degree angle, move the weights away from cleaner, or separate the first
two weights away from each other.

I consulter the owners manual for this model. This is what they suggest.

First, remove all of the air from the cleaner head and stop all air from entering the pool through the return lines. Also, if the head and hose are covered with bubbles, give the hose a good tug. This will release the air bubbles and allow the pool cleaners to settle son the bottom of the pool. Also, the cleaner head may actually be being lifted off the bottom of the pool by the hose or the pressure in the return lines. Make sure that the hose stays untangled and the pressure from the return lines is not too low (not enought pressure to power) or too high (too much pressure that cause the unit to lift off the floor).

If these pool cleaners are not getting proper suction on the pool floor or wall, it is most likely a problem with the flapper. Make sure that your flapper does not have an debris or tears that would prevent a proper seal. Also, make sure that your water pressure is correct.

Yes just be sure the suction is not up to high. Many people beleve that in order for your cleaner to work it must zip around the pool. Your cleaner has hours of run time to clean the pool and a slow even pace is recomended. If youadjust your suction to the cleaner just till the pump starts to make noise then back it off your probally adjusted just right. If the suction is kept high so the cleaner runs fast it will pull harder to the floor wearing parts and causing the unit to work harder also wearing parts. The idea of the cleaner is to slowley go about cleaning your pool not the money out of your wallet. In my humbel oppion you have the best cleaner on the market. Ck with your local and see if they have any promotions. I worked in a store that ran a two weak promotion every summer called Hayward Days and we would give away wings and feet for the cleaners so people would bring them and we could keep them aware of the importnance of maintance over repair.

You have a clogged impeller