Someone on a duplicate of this question figured out why this is happening. https://bugs.mojang.com/browse/MC-197299?focusedCommentId=823730&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-823730
To fix my farm I linked each portal module to a portal in the overworld located in the centre of the module. (The red highlighted block is the block in the overworld that's linked to the nether)
I'm having the same issue in 1.16.3
Someone on a duplicate of this question figured out why this is happening. https://bugs.mojang.com/browse/MC-197299?focusedCommentId=823730&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-823730
To fix my farm I linked each portal module to a portal in the overworld located in the centre of the module. (The red highlighted block is the block in the overworld that's linked to the nether)
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