Rosetta spent almost two years at 67P, ending its mission with a hard landing on the comet's surface. During the spacecraft's journey and its two years at the comet, it captured almost 100,000 images. About 3/4 of them are from OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) and the rest are from the NAVCAM. (You can enjoy archives of its images here.)
These images are all being analyzed by scientists, and part of that analysis involves images from during and after perihelion. Perihelion is when an object is closest to the Sun, and scientists expect to see the most changes on the comet during that time. By comparing perihelion images with those following perihelion, they hope to gain a better understanding of how the comet evolves.
There's a lot going on 67P's surface. A fracture in the comet's neck region grew, patterns of circular shapes in smooth terrain changed over time, sometimes growing up to a few meters per day. There were also boulders moving across the surface. Some of them were tens of meters across and moved hundreds of meters. Other boulders left the surface completely and were ejected into space.

The arrows point to the approximately location of the ripple and scarp features to help guide the eye between images.

"So much happened on this comet between May and December 2015 when it was most active, but unfortunately because of this activity we had to keep Rosetta at a safe distance. As such we don't have a close enough view to see illuminated surfaces with enough resolution to exactly pinpoint the 'before' location of the boulder," Vincent said in a press release.

Comment: The mission talks of boulders but there's no evidence provided that ice was discovered on the comet, which would reflect similar findings by Japan: Asteroid Ryugu is surprisingly dry, Japanese spacecraft finds
OSIRIS images also show cliffs collapsing at different locations on the comet. One of those collapses involved a 70 meter wide segment of the Aswan cliff falling in July 2015.

"Inspection of before and after images allow us to ascertain that the scarp was intact up until at least May 2015, for when we still have high enough resolution images in that region to see it," says Graham, an undergraduate student working with Ramy to investigate Rosetta's vast image archive. "The location in this particularly active region increases the likelihood that the collapsing event is linked to the outburst that occurred in September 2015."

Perihelion puts a lot of stress on a comet. The huge increase in solar energy reaching the surface drives a lot of changes. This was especially true in 67P's southern hemisphere, which received most of the energy.
When scientist examine debris on the comet closely, they find that the surrounding regions near the collapse probably suffered other large erosion events in the past. The blocks of debris are in variable sizes, some up to tens of meters in size. But the boulders from the observed Aswan cliff collapse are only a few meters in diameter.
"This variability in the size distribution of the fallen debris suggests either differences in the strength of the comet's layered materials, and/or varying mechanisms of cliff collapse," adds Ramy.
Scientists studying 67P say that observing large events like cliff collapses opens a window into the internal structure of the comet. That knowledge helps piece together the overall history of the comet's formation.
"Rosetta's datasets continue to surprise us, and it's wonderful the next generation of students are already making exciting discoveries," adds Matt Taylor, ESA's Rosetta project scientist.
R.C.