By default, 3rd party library used in the background in order to provide MQTT connectivity (PubSubClient) had 128 bytes max payload length. This can cause problems like not receiving MQTT messages, problems with sending MQTT messages, etc.
We have to mention that 128 bytes are the max number of characters in header, topic, and payload.
Fortunately, there is a workaround. Just define build_flags in your platformio.ini file:
build_flags = -D MQTT_MAX_PACKET_SIZE=1024
This will increase the limit to 1024 characters, you can put less or more based on your application needs.