All theory. Go to some land offices and see what kind of answers you get. I predict 99% will say "No you can not, unless the owner of the land agrees." when the lease period will be longer than the usufruct or just simply or "No, not without the owners signature". The other 1% will say 'Yes, no ploblem.', and they would be wrong.

Applying your contention that you can extend the length of a usurfuct (the life of the holder)by giving a lease to your usurfuct that extends the length of time of your usurfuct suggests that the original owner and grantor of the usurfuct can lose his right of reversion upon the death of the holder of the usurfuct by the act of the holder of the usurfuct issuing a lease for longer than the usurfct is non-nonsensical. One cannot grant to another more right to property than you have been granted, regardless of what a government agency does. Granted, judicial remedy must be sought in such a case, however, land offices are a little more knowledgeable than most seem to give them credit for.

By applying your logic, a three year leaseholder could grant a usurfuct to a 21 year old.

No, THAT is not logical.

We are talking about the holder of the usufruct being able to issue a lease on the subject property. I believe that is possible (not without issues, but possible).

All theory. Go to some land offices and see what kind of answers you get. I predict 99% will say "No you can not, unless the owner of the land agrees." when the lease period will be longer than the usufruct or just simply or "No, not without the owners signature". The other 1% will say 'Yes, no ploblem.', and they would be wrong.

I would be greatly surprised if, even with the owner's approval, they agree to register a lease if there is already a usufruct.

Unrelated to the above comment: I remember I once asked an expat lawyer in Indonesia why he charged so much for easy visa work that anyone could do themselves. He answered that it ensured his clients were the people foolish and stupid enough to hire him. Less problems with them, more money....