Metformin SR was introduced by Merck to address the gastro-intestinal side effects of plain metformin, not necessarily to make it a once per day drug. The datasheet states that if control deteriorates on once per day Metformin SR, one should go back to the Metformin SR several times per day. Do you take all your SR at one time? If so, it might be worth going back to a smaller dose several times per day like when you were on plain metformin, ie the same metformin dose as originally but SR tablets rather than plain tablets.
best wishes
best wishes