If your provisional VAT ceases to apply from a certain month onwards, check the following points on the relevant formula (the ‘Fx’ button in the VAT sub-category):
Recurrence: this must be set to ‘monthly’ to carry over to all subsequent months.
Start date / end date: ensure that no end date cuts off the formula before the missing months.
Min/max amount: an incorrectly set upper limit may prevent the calculation from running for certain months.
Source categories: estimated VAT is calculated based on your input and output VAT categories. Check that these remain populated for the relevant months.
If everything is correct and the problem persists, please contact us, specifying the sub-category and the first month affected.
Reminder of settings: How do I manage my estimated VAT on Okimia (monthly VAT)?