How to know if it's actually broken?
Speed Buff/Debuff can come from toys worn, or for a brief period of time (up to 15sec) when Effects like oversexed, overheating, and pulsating are active.
Speed Buff/Debuff for Toys & mods using Toys can be seen on the Toys MCM - Active Effects/Buffs tab. If set to anything other than 0, you should expect your speed is currently altered. This won't show the brief effects.
Speed Buffs can come from various other mods. Frostfall for example will slow you when you have frostbite.
Most mods will show their buffs in the regular Skyrim Effects menu. Toys&Love cannot do this since its scaling buffs to Rousing and/or XP which are changing all the time.
If you are running on a corrupt save, you can be vulnerable to the problem. How do you end up with a corrupt save? See Golden Rule.
How to Fix?
In console... Type Player.ForceAV speedmult 100
Note: if a mod currently has an active speed buff, you will break that buff using this command. To properly fix, you need to remove the source of any speed buff first, so you are in a state where speed should be normal, then this command will set it to normal.