If I may humbly add something to check: the grass strip under ground and under obstacles with long rhizomes, to find another exit point. Even when it can not exit to the surface, because of the mulch.
Sometimes it finds an exit point along the way, but even if not, continues its path. So, for a blade of grass that you see, there can be dozens of underground rhizomes that have no outlet. To rip just the crest visible is not enough, because every piece of rhizome produces a new plant.
In the first picture, examining the maximum magnification, bottom left, just behind the leaves of the bush, you can see the blades of grass very close. Perhaps grass rhizomes are crawled under the mulch strangling the roots of blueberry.
If so, remove the mulch (and perhaps also the soil below) and check where they are rhizomes. If necessary, clean up the area and cover it again.