On servers, if a non-opped player is given a written book that uses the "score" JSON formatting, the written book will fail to format the page where the "score" JSON is used on.

How to recreated;

Step 1
Have two players join a Minecraft server in 1.15.2, one player having OP (Admin) permissions and the other player having no OP (Admin) permissions.

Step 2
Create a scoreboard objective of any kind. (Any objective name or type works, but I'll be demonstrating with a "dummy" scoreboard named "Test".)

/scoreboard objectives add Test dummy

Step 3
Set both player's "Test" scoreboard objective to 1. (Any value works, but I'll be demonstrating with the value of 1.)

/scoreboard players set @a Test 1

Step 4
Use the following command inside of a command block on the server once. (You can also send through chat, a function file, or the server console.)

/give @a written_book{title:"Test",author:"Test",pages:["[\"\",{\"text\":\"Hello\",\"color\":\"gold\"},{\"score\":{\"objective\":\"Test\",\"name\":\"@s\"}}]"]} 1

Step 5
Compare the newly given books between each other.

The intended result is that both players should receive a written book titled "Test", with the expected text inside to be the word "Hello" colored gold followed by the integer 1.

While the player with Admin permissions (OP) can see what is described above, the non-opped player see's failed JSON formatting code.

Step 6
Clear or store the given books in a chest and give both players OP (Admin) permissions.

Step 7
Run the exact same command as in Step 4.

Step 8
Compare the newly given books between each other.

As you can see; both players are now able to see the proper formatting inside the written book; the word "Hello" in gold followed by a 1.

Step 9
Clear or store the given books in a chest and revoke both players OP (Admin) permissions.

Step 10
Run the exact same command as in Step 4.

Step 11
Compare the newly given books between each other.

Both players should of received a written book named "Title" that has a page of failed JSON formatting code.

Conclusion
When using the "score" JSON formatting inside of a written book, players that are not OPed (Non Admins) have invalid permissions to use the "score" JSON formatting function, causing the JSON formatting inside the written books page to fail.