[FS#146] wndr 3700v4 and 4300v1 couldn't effectively use 128 nand flash space

[LEDE Bugs]

The following task has a new comment added:

FS#146 - wndr 3700v4 and 4300v1 couldn't effectively use 128 nand flash space
User who did this - Matias (Panderine)

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I have this issue with my WNDR4300. Indeed AROKH's build of OpenWRT fixed this for me (with no noticeable issues so far). Since I have null experience on building my own image and patching (besides defeating the purpose of running stable releases for me),how can I mount the missing partition in order to be able to install more software on my wnrd4300?
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=146#comment2082