1.8. I get the warning that "Main out" is near or has reached its limit.

This is because the offset value for Main Out is saturated. This can be fixed in the following way:

• Select "Main out " in the Offset Module
• Set the value to zero

The accumulation of offset at Main Out is actually a feature (that can be switched off, see below).
Normally when selecting "Unlock and restart scan" it is preferable to have the scan centered around the spectroscopy feature onto which the laser was initially locked. For this reason, the integrator value of the PID is transferred to the offset of the PID output channel. If you lock and unlock frequently, these offsets might add up until the total offset is saturated.

You can disable this feature in the PID tab under the "Settings" menu as shown in the attached screenshot.