The ICAEW reports that HMRC have identified discrepancies between losses shown on company tax returns (CT600) and the figures shown on the CT computations. These appear to have arisen as a result of a tax software issue, and the losses relate to changes, that have applied since the start of April 2017, in the rules for losses brought forward.
Full details are available on the ICAEW site, which also explains how HMRC propose to deal with the discrepancies.