This is nonsense fear mongering. It didn't "just wake up" in any sense, the reactivity has been monitored for years and did rise slightly after 2017-2019 as the New Safe Confinement reduced the amount of rain getting into the structure.

Here's a Reuters link of the same damn thing from six months ago: https://www.reuters.com/world/chernobyl-staff-record-rise-nu...

The journal article they refer to was from work done in 2020. https://pubs.rsc.org/en/content/articlelanding/2021/ta/d0ta0...

Work done to better understand the decay process going on in the post-meltdown structure is interesting, but none of it notes any real risk of significant criticality in the remnants of the core.