Pretty much what this means is that mate IS imminent (in real terms), SF just can't find it yet.
If you asked a stronger machine, it would spit out "Mate in 47", but as your computer can't reach this depth, it just 'knows' there will be mate without knowing a concrete number of moves, so it tosses out some fantasy numbers.

If you put a clearly won pawn ending on the board, where you aren't promoting in the next few moves (say you have a passive king, 2vs0 pawns, and distract the enemy king with one pawn to be able to queen the other), SF will also usually start out at something like +3 and then quickly climb to something like +59, without finding an actual mate yet.

Now if you have a position that isn't 1600% won and where this still happens (as an actual misevaluation), I'd be interested.. but the +130 or whatever is pretty normal. In general of course you shouldn't be taking those numbers too seriously..