Sauber introduced more advanced pitstop equipment for this year, but from the first race in Bahrain, it has encountered cross-threading issues on the wheel nuts, which led to disastrous pitstops over the first few races.
The Swiss team made some modifications and changed procedures to mitigate its hardware issues since Bahrain which has generally worked, but Sauber's pitstops are still generally slower than its midfield rivals.
Those problems have already proved immensely costly in the tightest midfield battle in years, with Sauber's Bottas and Zhou Guanyu still left without points while RB and Haas have already managed to get on the board.
Speaking ahead of this weekend's Chinese Grand Prix, Bottas said the team is introducing further modifications for the Shanghai race, but a permanent fix remained unavailable.
"It's a difficult situation and we shouldn't be in this situation, but we are and now we need to get it sorted," Bottas said.
"There are further modifications for this weekend, but it's not 100% fixed, so we know it's not yet our strength for sure.
"If anything, it can be our weakness, but we're trying. Let's hope that things go smoothly now."
Source: Autosport