Would working British shells keep Scheer from seeking battle?

Would the Germans avoid a full fleet battle if British shells were working properly?

No. The Germans already assumed British shells worked, although heavier damage during the action could make them break off earlier.

Better British ammunition would not by itself keep the High Seas Fleet in port. The Germans already assumed British shells worked when deciding to seek battle. Effective shells could change the action once firing began and German ships took damage. One open question is whether those losses would cause the Germans to break off earlier.