I’ve had this happen once in 1.12, if it helps.
Has been reported multiple times already… 
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I have the same issue here.
this may be fixed in 1.14 crosses fingers
… restarted the game, load my last savegame (clean from 1.14) and took a look into the Efficiency:
Some procedure some more times but everything worked fine so this is still very hard to reproduce :*(
Btw. The graph can exceed the 100%:
Nice… xD
Seems like it is still not fixed in 1.15
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