My personal speculation is that they are not pleased with its lack of capacity compared to the LCAC, specifically its (more or less) single file only carrying capacity. It is roughly the size of the LCAC and yet can only load 1/3 the number of vehicles. They may be looking for a Version 2 that gives more bang for the buck.
If that was all there was, they could have addressed it within the time frame we are talking about IMHO.
No, I believe there is something more fundamental, like propulsion, or maneuvering with such a load that is keeping them from building the proper propulsion capable of maneuvering adequately into the space they require.
If all they had to do was add some space to each side, and still maintain the requisite width for the entire vessel, then structurally that is not a difficult thing to do.
But if something is keeping them from being able to do that...and still meet the overall width constraint (ie the width of the LPD well deck) which is not as easy a thing to change, then that would explain the years and years delays.
We've been watching this since the first Type 071 was seen building in 2005 and then launched in 2006. For Pete's sake, it's been over ten years now.
Something fundamental is messing them over on this.
Some try and play down the need for the LCAC...but I do not buy it. Te thing has been built for them...and to carry four of them. They were real proud of this when they came out, how the Chinese had leap frogged up to a San Antonio style vessel with them.
And yet, they cannot take advantage of that now. It has to be eating them alive in the design areas.
anyhow...time will tell.