Yes you are right Real Madrid inconsistency is big worry. They mostly play very well but then their performance drops suddenly. Ancelotti needs to fix this problem. Issue might be due to problems between players or mistakes in Ancelotti strategy. If this is not resolved it will hurt players confidence and teamwork. Real Madrid has excellent players but their bench strength is uncertain. When key players get injured it greatly affects team performance. Ancelotti must find main reason for this problem and solve it quickly. If not Real Madrid chances of winning titles will be affected.
What you said is very logical for Real Madrid and also for Ancelotti to think carefully as the coach of Real Madrid. Because previously Real Madrid also had better reserve players so that their performance was not so affected when their main players were injured. But for this season it seems to be a bit different so Ancelotti needs to find out where the problem is and try to solve it as soon as possible before Real Madrid really loses the chance to become champions again this season because they are late in fixing the problems that are happening in the team.
No matter how bad Real Madrid's performance is, they can always get through the match quite well. Indeed, not many goals were scored, but at least this season Madrid has not been defeated in La Liga and in the Champions League they lost once, Madrid is considered unstable but still fine not much affected. In total there are 8 Madrid players who are injured but some will return sooner than expected. Courtois, Militao and Vini have been confirmed to have recovered this month. So they have enough time to prepare themselves against Barcelona in the first El Clasico match.