After the last update (1.16.100, not an option in the drop down) my world has been somewhat glitchy/laggy.  Most of it is not a big problem but I've been being attacked by invisible mobs.  I was swimming across a shallow river and started taking damage/being flung around, but could not see anything damaging me.  It was daytime.  A few blocks down the river was a frozen drowned and when I walked up to it, I could not hit it.  Later, I was walking around and come across a frozen spider that I could also not hit.  After a minute or two it disappeared.  Then I was digging a shaft towards the surface when I hit water.  I swam up and saw a drowned, started getting attached from multiple sides, retreated down the water and suddenly arrows started flying out of no where at me.  I tried hitting with my sword around the 3x3 square space I was in with no luck hitting anything.  I did search for similar issues but the old bug seemed to have to do with recent player death and I haven't died in a while now.