When a grubfruit plant converts between it's spindly and non-spindly version, the harvest setting that's been applied to them is reset back to the default. This is most likely because the plant is being replaced by it's alternative form.
No files are needed to report this issue.
Find a spindly grubfruit and enable harvesting on it. Expose it to a Sweetle to convert it into a grubfruit. Check the harvest setting of the new grubfruit.