There has been extra flaring from the other chemical plant sharing the site.
Mossmorran Action Group said the closure on 15 August had caused a knock-on effect to the Shell Fife NGL plant.
Shell said it expected short periods of elevated flaring, which could be smoky. Plant manager Theresa Waddington said she regretted that it could last a month.
After the temporary shutdown of ExxonMobil’s neighbouring Fife ethylene plant (FEP) plant, Shell said it was having to adjust its operations to keep processing.
Ms Waddington said the flow of gas to the plant from the North Sea had been reduced to allow Shell to stop the supply of ethane to FEP while it was not operating.
“Due to these unusual circumstances, there have been occasional, short periods of minutes of low volume flaring in the Fife NGL plant’s elevated flare,” she said. “The Fife NGL ground flares have also been in use.”
She added: “I expect this pattern to continue, regrettably, as we manage the situation.”