On May 13th I captured another one of such instances, after first capturing it on May 5th (see report here, 2nd part of that post).
On May 5th I captured it decreasing in brightness froma prominent brightness peak. This time, I captured it increasing in brightness towards a prominent peak near 21:44 UTC, with a hint of the start of a decrease later. Here is a selection of images, all spaced 1 minute apart:
The first 11 images in the series yield the curve below (I did not include the rest of the images, as they are all saturated)
Both this May 13 and the earlier May 5th flaring occurred close to the moment that the sun, observer and satellite lined up, indicating it is probably due to reflection on the solar panels.