In today's average instance size of Jira Data Center having the capability to create more than one Rank field is not a good idea. Having more than one rank field is generally not useful and causes heavy performance issues like Reindexing becoming very slow etc.
Multiple Third-party plugins ( viz., Botronsoft - Configuration Manager for Jira) can introduce new Rank without active knowledge of customers followed by major performance impact on Lock and Reindexing due to rankInitially and backoff mechanism. Also, it can cause issues such as not being able to re-rank issues on Agile boards.
There should be just one Rank field (Default). User or third-party import tools shouldn't be able to create any new Custom field of "Global Rank" Type.
Please check your Lexorank Management page on the Jira UI and if you see more than one Rank field, follow this kb to Manually Remove duplicate Rank fields in Jira server