Some to solve a problem with a table issue in MSSQL

We have an issue with a table in our key database. We use MSSQL 2012 (express) and have an MS Access front end. On a seemingly random basis, one table in the database will not allow updates. It will allow you to read and append, but not update. All other tables work fine, even when this issue is occurring.
This can happen multiple times a day, but can also go a week or 2 without occurring.
We cannot find any logs or information on what is causing this.