Filled in T2125 properly, T1 line 162 shows correct gross amount but nothing on T1 line 135, . Why is this happening, I have had no problems in the past 9 years ?

You likely claimed enough business expenses to reduce your income, then if you used Business Use Of Home were able to reduce the amount to Zero. 

Depending on which version of TurboTax you are using, you should be able to see on the T2125 Summary if this is the case.