Given the spiky, confrontational relationship that has existed between Red Bull and Renault for several years, I think the reliability of the Red Bull team is going to decline rapidly from here on out. Toro Rosso suffered badly at the end of last year when Renault declined to supply any newer-spec powerplant components, on the grounds that they were focussing all R&D on 2018. We saw the TR cars being fitted with all manner of high-mileage powerplant components at the end of the season.
The underlying issues are:
(1) Renault is trying to do F1 on a budget which is not big enough. There is a story circulating of how, when Renault were seriously wondering whether they should even continue in F1 because not enough money was on offer, Ron Dennis launched into a blunt series of comments at a leadership meeting, effectively telling Bernie and the others to give Renault the ****ing money. I think, however, that Renault is operating like Ford in its last 10 years in F1, a day late and few million dollars short.
(2) Renault never wanted to supply Red Bull in the first place, and only did so because the complicated set of agreements between the FIA and the powerplant suppliers forced them, under the terms of the contract with LibertyF1, to supply Red Bull. That is not a recipe for a harmonious relationship. It looks more like a shotgun wedding to me. The TAG Heuer badging of the powerplant tells its own story.
The relationship between Red Bull and Renault is broken, it has been broken for years, and I expect to see and hear a lot of light, heat and sound between those two parties before the end of the season. They may dress it up in marginally more polite language, but I think the prevailing sentiment on both sides is not much above "well ***k you" right now.