Are you sure these aren't the same glitches in the data that Gridwatch Templar is using? This has glitched before, as both Gridwatch and Gridwatch Templar are unofficial, I believe, so rely on scraping data from Elexon.
Edited to add:
Just looked closely at the Gridwatch Templar pumped hydro and it shows the same pattern of glitches (in the blue trace), and as pumped hydro cannot respond that quickly I suspect there is an issue with the way that data has been scraped from Elexon:
Yes, these are glitches, happens fairly regularly. The most common one is when the sun turns off around 10am and doesn't turn back on until around 2pm on the solar trace. I think that happens when Sheffield Uni forget to pay their internet bill.