Charactermancer level+ only lets Cleric,Druid add # prepared spells to spell list

Cleric character, leveling up from 2 to 3. DnD5e rules state cleric has access to entire list of available spells for levels that they have slots. From this list, they select prepared spells. When a Cleric levels up from 2nd to 3rd, they should get access to the entire 2nd level Cleric spell list from which to choose prepared spells. Charactermancer does not do this. Instead it allows the character to pick spells from the list to add. This character has a high wisdom, so the # of prepared spells they have is 8. Charactermancer allows this player to select 8 spells from the 1st and 2nd level Cleric spell list to add to their character sheet, when instead it should add the entirety of the 1st and 2nd level Cleric spell list. Is there a way I can change the # of spells Charactermancer lets my player choose, or are we going to have to manually keep adding the others in? I have seen the same problem with Druid characters as well. Please comment/fix.

This isn't a bug, but intentional.  Spell entries spawn a huge amount of attributes on the sheet.  Some of these attributes are interacting with the javascript sheetworker system to autofill/adjust some of those attributes based on character stats.  You pile enough spells on a sheet, and you are likely to get a very laggy sheet or one that won't open.  Do this on enough sheets in a game and you may impact the performance of the entire game. I don't play 5E, so I'm not as familiar with that sheet.  In a test game, it looks like each spell entry on the spells tab spawns up to around 19 attributes.  If that spell also has an attack listing, then you can add up to an additional 25.  So a single spell can be adding 44(ish) attributes to the sheet.  You really don't want to add all possible spells to a sheet if you want it to continue working well.  Might not be too bad at low level, but every time you add another spell level, you will be getting quite the increase to attribute/sheetworker load on that character.

So: "Our computer is too slow"?

We were just discussing this yesterday in our game. I gather from this that the servers are too slow to handle doing spells properly. (definitely emphasized by the instability seen yesterday) If it were simply a matter of concern that the end users computers are lacking then it should be available as an optional thing. I personally have no delays with all my spells on several characters and only 2 of my 24 threads available for roll20.

Not sure it is server limitation, or a browser limitation (how much can one browser tab handle?).  If it works for you, that is great.  Load everything.  But it is best that Roll20 not do that by default, because that definitely isn't the experience of everyone.