There is also another source of afternoon fatigue if there is no history of long term gut issues.

Increasingly B12 Deficiency is being seen in Seniors. If you separate the most common source of B12D for vegans, then a possible source of B12D is age - in that the process of absorbing B12 from food sources tends to be less functional. As the number of a protein called Intrinsic Factors that transmits into the blood stream decline significantly.

The best solution for this reduction in B12 transfer capability is periodic B12 injections. How much and how often will vary for each person’s causalities and can take a while to titrate the best schedules.
Chris47 -