The central bank statement said the problem was caused by overwhelming online transactions of one bank affecting other networks and preventing online banking on smartphones. 
The central bank asked banks to temporarily shutdown their network traffic to enable it to upgrade its own systems. 
Now most banks had resumed online banking services normally, said the central bank. 
A source said the problem was caused by Kasikornbank, which has largest online banking market share.

Central bank: online shutdown resolved

The Bank of Thailand says most banks have now resumed online banking services after networks crashed on Friday morning.