I can think of three reasons it would do that.
1. You came back after the change to weapons which now have a base attack speed rather than an increase.
2. You were watching it while attack speed boost was on, and it ran out, which drops it back to default.
3. Rampage increases your stats, amongst them your attack speed, it would also drop it to default if it runs out.
Took a look at the formula, seems like the ring is not giving the right amount. Will fix that in the next update. Thank you for notice!