This isn't exactly a bug but I'm trying to figure out how to add an akashic tome which is a book that holds other guide books, to a kit. I used craft tweakers /ct hand command and copied the item and it's nbt but that hasn't worked for me and I don't really understand json/nbt very well. Would it be possible to add a command that takes whatever a person is holding in their hand with its nbt and adds it to a kit? I saw you mention you're adding a gui to the 1.16 version and suggested that people use the gui on 1.16 and than use the generated file on 1.15 but this tome item isn't available on 1.16 😅

{
"kits": {
"tome": {
"duration": 3600,
"items": [
{
"name": "akashictome:tome",
"quantity": 1,
"nbt": ".withTag({"akashictome:is_morphing": 1, "akashictome:data": {powah: {id: "powah:book" as string, Count: 1}, engineerstools: {id: "patchouli:guide_book" as string, Count: 1, tag: {"patchouli:book": "engineerstools:engineerstools_manual" as string}}, planttech2: {id: "planttech2:guide_overview" as string, Count: 1, tag: {Damage: 0}}, golems: {id: "golems:info_book" as string, Count: 1}, immersiveengineering: {id: "immersiveengineering:manual" as string, Count: 1, tag: {"akashictome:displayName": "{"translate":"item.immersiveengineering.manual"}" as string, "akashictome:is_morphing": 1, display: {Name: "{"translate":"akashictome.sudo_name","with":[{"color":"green","translate":"item.immersiveengineering.manual"}]}" as string}}}, rftoolsbase: {id: "rftoolsbase:manual" as string, Count: 1, tag: {"akashictome:displayName": "{"translate":"item.rftoolsbase.manual"}" as string, "akashictome:is_morphing": 1, display: {Name: "{"translate":"akashictome.sudo_name","with":[{"color":"green","translate":"item.rftoolsbase.manual"}]}" as string}}}, woot: {id: "patchouli:guide_book" as string, Count: 1, tag: {"akashictome:displayName": "{"translate":"item.woot.wootguide.name"}" as string, "patchouli:book": "woot:wootguide" as string, "akashictome:is_morphing": 1, display: {Name: "{"translate":"akashictome.sudo_name","with":[{"color":"green","translate":"item.woot.wootguide.name"}]}" as string}}}, valkyrielib: {id: "valkyrielib:guide" as string, Count: 1, tag: {"akashictome:displayName": "{"translate":"item.valkyrielib.guide"}" as string, "akashictome:is_morphing": 1, display: {Name: "{"translate":"akashictome.sudo_name","with":[{"color":"green","translate":"item.valkyrielib.guide"}]}" as string}}}, engineersdecor: {id: "patchouli:guide_book" as string, Count: 1, tag: {"patchouli:book": "engineersdecor:engineersdecor_manual" as string}}, securitycraft: {id: "securitycraft:sc_manual" as string, Count: 1, tag: {"akashictome:displayName": "{"translate":"item.securitycraft.sc_manual"}" as string, pages: [], author: "Geforce" as string, "akashictome:is_morphing": 1, display: {Name: "{"translate":"akashictome.sudo_name","with":[{"color":"green","translate":"item.securitycraft.sc_manual"}]}" as string}, title: "SecurityCraft" as string}}}})"
}

  ]
}

}

Try to use some JSON Parser online to check if your json is correct, also JSON Stringify might help you.

I used this tool to stringify the json: https://onlinejsontools.com/stringify-json
and this tool to validate it: https://jsonlint.com/?code=

Still can't get the kit to work in game.

Here's my default kits (changed to .txt to upload to github)
default_kits.txt