Pensionable earnings and insurable earnings can easily be different, especially if there are benefits or if the payroll for the year is large.  Remember that, even though they are both dealt with in payroll, they actually come from two different pieces of legislation - the pensionable earnings is part of how CPP works, and the insurable earnings is part of how EI works.

First, there are some types of taxable benefits that are subject to tax and CPP but not EI.  If you have any of these benefits, pensionable earnings will be higher than insurable earnings.  To see which these earnings are, look at the benefits chart in the CRA benefit guide (Guide T4130).

Second, the maximum amounts are different.  For 2020, maximum pensionable earnings were $58,700, while maximum insurable earnings were only $54,200.

I do understand that Insurable Earnings and Pensionable earnings are based on different incomes, but these employees would not have any earnings that are pensionable but not insurable.  As I mentioned in my question there are no benefits to explain the difference.
The difference is all in one pay period where I had to manually adjust the deductions.

The last I heard, EI Insurable Earnings is back calculated in Sage 50 based on EI amount entered on the paycheque when in manual mode.  This can alter the numbers based on year end Gross.  I would just edit the T4 amounts on the ledger to what you think is correct considering what C. White mentioned regarding upper limits and potential EI excluded earnings.

Also don't forget about waiting until the update at the end of January is installed before you print your T4's if you released vacation pay on each cheque during 2020.

The last I heard, EI Insurable Earnings is back calculated in Sage 50 based on EI amount entered on the paycheque when in manual mode.  This can alter the numbers based on year end Gross.  I would just edit the T4 amounts on the ledger to what you think is correct considering what C. White mentioned regarding upper limits and potential EI excluded earnings.

Also don't forget about waiting until the update at the end of January is installed before you print your T4's if you released vacation pay on each cheque during 2020.