Ferrari appears to have suddenly lost part of its power advantage, following the FIA's initiative of adding a second sensor to the SF71-H's power unit.
Both Mercedes and Renault queried the governing body earlier this year over Ferrari's sudden surge in power and performance.
The FIA subsequently investigated the Scuderia's dual-battery energy storage system, installing a sensor to monitor the unit's process but ultimately finding nothing illegal.
However, according to Germany's Auto Motor und Sport, a second FIA sensor was fitted recently, and this apparently resulted in a sudden drop in performance per GPS data collected by rival outfits.
"We can see it clearly in our GPS measurements," admitted Renault team boss Cyril Abiteboul.
Mercedes engine guru Andy Cowell insists Ferrari "still has plenty of power", but the data still point a drop off of power under acceleration, a reduction that may have impacted the Scuderia's performance in the last two races.
"If they have less power, they may not be able to drive the wing adjustment from before and have to return with the downforce," added Abiteboul.
When asked about Ferrari's mysterious power drop in Singapore and Russia, 2016 world champion Nico Rosberg told Sport1: "I don't think we can judge that.
"Let's wait for the next races. If it's still the case, then we can say 'Ok something has happened'. But it's too early for that," he added.
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