Revenue has apologised for ongoing intermittent performance problems with its main import system.
This has led to difficulties and delays for businesses trying to bring goods into the country since the end of the Brexit transition period.
Tom Talbot, head of the Revenue Customs operation at Dublin Port, said degradation issues with its Automated Import System (AIS) were occurring mostly at times of peak processing.
"This results in delayed responses to declarations and other messages lodged by the trade," he said.
""We are very conscious of the impact this has had on trade and business moving goods and we apologise for the inconvenience caused," Mr Talbot added.
Freight transporters and hauliers have complained of significant issue with the AIS in recent weeks, with the Irish Road Haulage Association (IRHA) branding it not fit for purpose.
Eugene Drennan, President of the IRHA, said it was taking four to five hours in some cases to get declarations processed.
Freight handling businesses have expressed frustration that the issue is particularly acute at the times they normally file their paperwork, forcing them to have to work late into the night instead.
Speaking at a multi-agency post-Brexit update at Dublin Port, Mr Talbot said one of the contributing factors to the problems is the growth in business levels of large filers with lots of small consignments, a business model that has increased significantly with the move to online shopping since the start of the pandemic.
"Revenue is working very closely with our software provider to increase capacity at peak processing times," he added.
"At the same time Revenue is working with the large providers themselves to develop tailored solutions that will facilitate their business model and ensure that other goods and traffic is not adverse impacted by peak load processing delays," he said.
Mr Talbot claimed that the initial indications are that the steps taken so far are having a positive impact on the processing performance and said the focus would continue on improving that performance further.
The briefing also heard that in the last 24 hours, 86% of freight vehicles arriving into Dublin Port from the UK were given a green routing, meaning they did not need to stop for documentation or physical checks.
However, Eddie Burke from the Department of Transport said it remains the case that volumes are still around 50% of what they were this time last year, a level they have been stuck at for several weeks since the start of January.
This is a matter of concern, he said, and a lot of work is ongoing to examine how to get it back up to the levels normally seen.
The reduced volumes continue to be influenced by pre-Brexit stockpiling, suppressed demand due to the pandemic and the increased use of direct routes between Ireland and continental Europe, he stated.
Importers, though, say ongoing and persistent problems with the new customs and other post-Brexit procedures are leading to reduced trade between the UK and Ireland.
"We would like to see it come back up to those levels," Mr Burke said, adding that volumes are coming back slowly.
But despite the reduced importation of goods from the UK, the Department of Enterprise said it remains the case that the retail supply chain continues to function well.
"We continue to be assured by retailers and grocery distribution importers and distributors that supply chains are robust and strong and shelves at store level remain well stocked," said Declan Hughes, Assistant Secretary from the Department of Transport.
He added that isolated issues are being worked through and Bord Bia is working in some cases to increase domestic supplies of certain goods.
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Hazel Sheridan, from the Department of Agriculture, said its operations at Dublin Port continue to operate well within the capacity of the border control posts.
She said as time goes on, importers and hauliers are becoming more familiar with the requirements, things are improving all the time as a result and the department is ready for an increase in business.
Tom Talbot said 1.8 million customs declarations had been processed by Revenue in January, compared to 1.6 million in the whole of 2020.
Prior to the end of the transition period, Revenue had predicted that it would have to process 20 million declarations a year as a result of the UK leaving the single market and customs union.
Mr Talbot added that Revenue has set up dedicated email addresses and a 24/7 helpline to assist anyone struggling with the new procedures.
But hauliers and importers have complained that they find it very difficult to contact or get answers from state agencies in relation to the new requirements.