Attempting to use the Coxme Function on a Mixed Effects Model

Question

I have a mixed model of several different variables that I would like to run a boxcox function on to get an idea of the appropriate lambda value. After some research I found that the coxme function may be more appropriate for a mixed model. I keep getting errors when attempting to run the coxme function on my model.

Here is my original attempt:

coxme(lmer(WAKDE~
        Avg.AS.Temp+
        Avg.Temp.Seasonality+
        Avg.PPT.Seasonality+
        Avg.Winter.PPT+
        Avg.Summer.PPT+
        Avg.MSAVI2+
        Avg.Timelag.MSAVI2+
        Avg.Timelag.winter.PPT+
        Avg.Timelag.summer.PPT+
        Avg.TRI+  
        (1|Site/ID),data=Env.HR))

This resulted in the following errors:

boundary (singular) fit: see help('isSingular')
Error in if (n == 0) stop("No observations remain in the data set") : 
  argument is of length zero

After some researching I managed to find this workaround

coxme(lmer(WAKDE~
        Avg.AS.Temp+
        Avg.Temp.Seasonality+
        Avg.PPT.Seasonality+
        Avg.Winter.PPT+
        Avg.Summer.PPT+
        Avg.MSAVI2+
        Avg.Timelag.MSAVI2+
        Avg.Timelag.winter.PPT+
        Avg.Timelag.summer.PPT+
        Avg.TRI+  
        (1|Site/ID),data=Env.HR,
        lmerControl(optimizer ='optimx', 
        optCtrl=list(method='nlminb'),
        check.conv.singular = .makeCC(action = "ignore",  tol = 1e-4))))

Which gave me the following error:

Error in if (REML) p else 0L : the condition has length > 1

This led me to my current attempt:

coxme(lmer(WAKDE~
        Avg.AS.Temp+
        Avg.Temp.Seasonality+
        Avg.PPT.Seasonality+
        Avg.Winter.PPT+
        Avg.Summer.PPT+
        Avg.MSAVI2+
        Avg.Timelag.MSAVI2+
        Avg.Timelag.winter.PPT+
        Avg.Timelag.summer.PPT+
        Avg.TRI+  
        #Site+
        (1|Site/ID),data=Env.HR,
        REML=FALSE, 
        lmerControl(optimizer ='optimx', 
        optCtrl=list(method='nlminb'),
        check.conv.singular = .makeCC(action = "ignore",  tol = 1e-4))))

This code results in the following error:

Error in if (n == 0) stop("No observations remain in the data set") : 
  argument is of length zero

And I can't seem to find a fix for this one. Any ideas about how to fix it, or if there's a more appropriate way to estimate a lambda value for a mixed effects model? Thanks!