This is interesting.
A published paper suggests that our ancestors almost went extinct between 930 000 and 813 000 years ago. During this 117 000 years the population size is estimated at less than 1300 individuals.

Ice age, unfavourable hunting, and generally tough times are assumed the cause.

I'm not qualified to judge the techniques used to arrive at this estimate, but I find that very interesting.

Some details. Text on this diagram in the paper which is, DOI: 10.1126/science.abq7487.

Fig. 5. Schematic diagram of human population size history. Both African (light green) and nonAfrican (light blue) populations are presented. The width of the boxes represents the effective population size (i.e., the number of breeding individuals) with naturally occurred fluctuations. The occurrence time of the out-of-Africa dispersal and the divergence between African and non-African populations are indicated. The gray-shaded time duration indicates the Early to Middle Pleistocene transition between 1250 and 700 kyr BP. The red arrow indicates the peak of glaciation during the transition (i.e., the 0.9 Ma event). The ancient severe bottleneck inferred in this study is highlighted. The gap in the available African hominin fossil record and an indicative chronology for H. erectus, the LCA, and H. sapiens are shown. The estimated time period in which two ancestral chromosomes (chromosome, Chr.) fused to become one is also shown on the right.