Profile Confidence Interval in lmer model .

When I fit lmer model with my data , there is no warning message. But when I tried to construct confidence interval by `confint` , it shows the following warning message :

Warning messages:
1: In FUN(X[], ...) : non-monotonic profile
2: In nextpar(mat, cc, i, delta, lowcut, upcut) :
Last two rows have identical or NA .zeta values: using minstep
3: In FUN(X[], ...) : non-monotonic profile

Is there any way to overcome the warning message , that is, is there any argument(option) which can remove the problem ? I have used the argument "control=lmerControl(optCtrl=list(maxfun=20000))" .

fit <- lmer(Y~X+Z+X:Z+(X||group),data=dat,control=lmerControl(optCtrl=list(maxfun=20000)))

Any help is appreciated. Many Thanks! Regards.