wrote unit test which reproduced the problem

src/grant-fund.ts

@@ -1,5 +1,4 @@
 import { Address, Bytes, ethereum, log } from '@graphprotocol/graph-ts'
-// import { log } from "matchstick-as"
 
 import {
   DelegateRewardClaimed as DelegateRewardClaimedEvent,

src/utils/convert.ts

@@ -23,17 +23,16 @@ export function addressArrayToBytesArray(addresses: Address[]): Bytes[] {
 }
 
   export function bigIntToBytes(bi: BigInt): Bytes {
-    // return Bytes.fromByteArray(Bytes.fromBigInt(bi))
-    return Bytes.fromByteArray(ByteArray.fromBigInt(bi))
+    const unsigned = BigInt.fromU64(bi.toU64())
+    return Bytes.fromByteArray(Bytes.fromBigInt(unsigned))
 }
 
 /***************************/
 /*** To BigInt Functions ***/
 /***************************/
 
 export function bytesToBigInt(bytes: Bytes): BigInt {
-    // return BigInt.fromUnsignedBytes(bytes)
-    return BigInt.fromSignedBytes(bytes)
+    return BigInt.fromUnsignedBytes(bytes)
 }
 
 // converts a BigDecimal to a BigInt scaled to WAD precision

src/utils/grants/distribution.ts

@@ -1,5 +1,4 @@
 import { Address, BigInt, Bytes, dataSource, log } from "@graphprotocol/graph-ts"
-// import { log } from "matchstick-as"
 
 import { GrantFund } from "../../../generated/GrantFund/GrantFund"
 import { DistributionPeriod } from "../../../generated/schema"

tests/convert.test.ts

@@ -0,0 +1,16 @@
+import { BigInt } from '@graphprotocol/graph-ts'
+import { assert, describe, test } from "matchstick-as/assembly/index";
+import { ONE_BI } from "../src/utils/constants";
+import { bigIntToBytes, bytesToBigInt } from "../src/utils/convert";
+
+  describe("Conversions", () => {
+    test("Reliably convert integer contract values to bytes", () => {
+        const one_bi = BigInt.fromU32(1)
+        const one_number = 1
+        assert.bigIntEquals(one_bi, BigInt.fromI32(one_number));
+
+        const one_bytes_from_bi = bigIntToBytes(one_bi);
+        const one_bytes_from_number = bigIntToBytes(BigInt.fromI32(one_number));
+        assert.bytesEquals(one_bytes_from_bi, one_bytes_from_number);
+    });
+  });