Trial value wasn't being initialised big enough for very low difficulty, also development should not have been there but I don't think it was doing anything

js/util_worker_tasks.js

@@ -46,7 +46,6 @@ function calcPoW(
   ttl,
   pubKey,
   data,
-  development,
   difficulty = undefined,
   increment = 1,
   startNonce = 0
@@ -56,7 +55,6 @@ function calcPoW(
     ttl,
     pubKey,
     data,
-    development,
     difficulty,
     increment,
     startNonce

libloki/proof-of-work.js

@@ -77,9 +77,7 @@ const pow = {
 
     let nonce = new Uint8Array(NONCE_LEN);
     nonce = pow.incrementNonce(nonce, startNonce); // initial value
-    let trialValue = pow.bigIntToUint8Array(
-      JSBI.BigInt(Number.MAX_SAFE_INTEGER)
-    );
+    let trialValue = new Uint8Array([255, 255, 255, 255, 255, 255, 255, 255]);
     const initialHash = new Uint8Array(
       await crypto.subtle.digest('SHA-512', payload)
     );