I have been cleaning this pool for a year now. I never had an issue with the vacuum untill a few months ago. I use the filter setting to vacuum the pool and I always keep the skimmer basket in while I vacuum (so I don't think that the pluming is clogged). It starts out with good suction for about five minutes then gets real weak. The only way I get it to work better is to put in on recirculate for a few seconds then put it back on filter. It works for a few minutes but then gets weak again. I have to repeat the actions above untill the pool is vacuumed and it is getting really old.
Again, I don't think the pluming is clogged. The skimmer basket is not full (I am just trying to vacuum dirt, no leaves). The pump basket is clean. The filter works fine in every day filtering, it also wastes and backwashes fine.