Custom report sorting

I have used a customised customer contact list for 5+ years to contact my customers when they should be due to order goods. To do this (as a work around as there is no specific date field for this) I have used the Notes field in the customer record with the first line being "CONTACT YYYY/MM", which could then be sorted in ascending order, so that I could contact customers grouped in the relevant month, e.g. CONTACT 2023/09 (for contact in September 2023). Other first lines included "HQ / ACCOUNTS ONLY", "NO CONTACT", "PASSED TO NTR" & "TRADE", which meant that all customers to be contacted by year & month appeared at the top of the report, then customers appeared in groupings based on the alphabetical first letter of the first line, i.e. as listed above. However, since July when I have added new customers (with notes in the same format), they have gone to the bottom of the report and are not sorted by the correct date, but alphabetical on the company name. I have spoke to support and it seems like an update has caused this issue. Can the system be put back to how it was?