You did not specify whether or not this is a channel that has been narrow banded.
Most transceivers default to sending the PL tone at a deviation that is a function of the voice deviation limit. Back in the day, the generally accepted level for PL was 750 Hz, though most receivers would correctly decode PL at a value as low as 400 Hz.
In theory, once you narrow band a channel, the transceiver should send the tone at 375 Hz. However, if your listeners are still programmed for wide band, this may be too low to function their tone decoders, and I've heard reports (but never observed the phenomenon myself) that some older radios have trouble decoding narrow band (sent) PL even when their receivers have also been programmed for narrow band.
If you have the capability, try increasing the tone deviation.