If it’s happening on all MBC sites, then it’s definitely a problem with your MBC parameters. Which band is UL and which is OL?
Check and make sure that BCCD is set to yes on the 1800 channel group (use RLCHP).
Also check your channel allocation profile (CHAP) to make sure you have not excluded any of the subcells from Immediate assignment. (CHAP 5,11 or 12).