Psyllium clumps because it hydrates too well, too fast, on the outside.
When dry psyllium hits water, the surface can swell immediately and form a gel coat. That gel coat blocks water from reaching the dry centre. The result is a soft lump outside and dry powder inside. Anyone who has stirred isabgol slowly into a glass has seen this happen.
The fix is not complicated, but it needs timing. Use a larger glass of water. Add psyllium while stirring, not after it settles. Stir briskly or use a shaker. Drink soon, before the mixture gets too thick. Do not let it stand like tea.
Temperature, particle size and other ingredients also matter. Very fine powder may hydrate faster. Sugary or acidic drinks can change the experience. Milk may feel heavier than water. A smooth fibre supplement should ideally disperse before it fully gels.
If clumping keeps happening, reduce the serving size and build slowly. More powder in less water usually makes the problem worse.
Psyllium is not difficult because it is weak. It is difficult because it is powerful. Better mixing helps the fibre do its job without making the routine unpleasant.
Clumping is a mixing problem, not a psyllium problem. Fix the stir, the water and the timing, and the lumps mostly disappear.