ZURICH (Reuters) -UBS is delaying the migration of some super-rich Credit Suisse clients to its own platforms by several months, sources told Reuters, a rare setback in an integration process that has so far progressed relatively smoothly.

The delay signals that the bank could struggle to meet its end-of-March deadline to complete the migration of all clients with an account in Switzerland. UBS is still aiming to meet that target and when asked for comment on Monday, a UBS spokesperson said the migration in Switzerland was "proceeding as planned".

The Zurich-based lender's emergency takeover of Credit Suisse in 2023 led to the largest bank merger since the 2008/09 financial crisis and a vast, multi-year integration involving more than one million clients. UBS has said it will "substantially" finish the integration by end-2026.

Investors are watching closely as the integration of technology and data is a key part of UBS' pledge to squeeze $13 billion in cost savings from the merger. Moving clients onto new tech platforms has proven a major headache in the past for big lenders such as Deutsche Bank.

UBS has postponed the transfer of Credit Suisse wealth management clients including ultra-high-net-worth individuals to the first quarter of 2026, according to six people familiar with the matter.

Some of the very rich clients were initially scheduled for migration in September and have been delayed to January, one of the people said.

Another client migration wave is now planned for February, one of the six sources and an additional person said, and another one for March, one of these people said.

Customers booked through Switzerland include locals and those from elsewhere but with a Swiss account.

GLITCHES IN EARLIER CLIENT TRANSFERS

The exact reasons for the delay are unclear, but one of the sources said integration teams were overworked, and a shift before year-end could have complicated tax filings for clients.

UBS may have pushed back clients in this critical segment after some glitches emerged in transferring less wealthy sets of customers, two of the six sources said.

Problems have included transactions for clients that had to be revised and systems that were not immediately available, the people said, without going into specifics. Reuters could not establish the scale of such glitches.

UBS did not respond to questions on glitches.

Separately, one of the six sources and the seventh person said UBS was concerned that outflows of former Credit Suisse clients may exceed expected levels as accounts are moved to its systems.

UBS said when presenting third-quarter results last month that it was on course to deliver the integration as announced, having made "excellent progress" with more than two thirds of Swiss-booked client accounts already migrated.

Bank mergers are hugely complex and can cause major problems for acquirers.

Deutsche Bank's 2008 purchase of Postbank, for example, became the source of consumer complaints, regulatory scrutiny and costly lawsuits. The final technology integration finished in 2023.