A new booking-system limit was reported in late October: only two availability checks per NIE per day. The situation became particularly difficult in Barcelona.
According to practitioners, an additional rate-limiting mechanism was introduced in the fingerprint appointment system at the start of the week. Availability checks per NIE dropped from about 50 to two per day, and the limit applies even to viewing free slots, not only to booking.
At the time of reporting, finding an appointment in Barcelona was very difficult. For some Cuenta Propia procedures the situation differed: once the permit was approved, the appointment was assigned automatically.
Practical takeaway: when planning the TIE, allow for possible booking delays and distinguish between procedures that require self-booking and those with automatic assignment. This limit should be re-checked before relying on it.