GAMM convergence issue with temporal covariate

Hello,

I am working with a fairly simple model:

gamm(sv~s(day,bs="cr")+range+s(time,bs="cc"),correlation=corARMA(p=2,q=2)

In which day is Julian Day over one month, range is tidal range, and time
is coded 1-24 for hour of day.

I continually have singularity convergence problems with this model (the
error is:  nlminb
problem, convergence error code = 1 message = false convergence (8).

Increasing iterations does not help. When I run msVerbose I notice that
"day" covariate output values (there are two but I'm not completely sure
how to interpret them) keep increasing until the convergence errors occur.
I have also noticed that setting k=5 for the "day" covariate does not help
the convergence problem, but k=9 does (the default is 10) or k =20. I would
greatly appreciate any advice or recommendations on what may be causing the
problem.

Thank-you very much,
Hannah