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I'm not sure. With your 200 SP you should be fine normally, it could be that the blockchain is getting more spam than usual. It's unclear.

Judging from some of the other replies here it seems that I'm not the only one it's happened to. Whatever it is is very interesting, hopefully it's not going to be much of a problem in the future.

It seems there might be a few little gremlins playing around with the inner workings of steemit right now, I remember seeing last week someone post about a resteem that disappeared.