diff --git a/services/web/app/src/Features/SplitTests/SplitTestSessionHandler.js b/services/web/app/src/Features/SplitTests/SplitTestSessionHandler.js
index 7510b6686a..1b9bf5597f 100644
--- a/services/web/app/src/Features/SplitTests/SplitTestSessionHandler.js
+++ b/services/web/app/src/Features/SplitTests/SplitTestSessionHandler.js
@@ -60,12 +60,18 @@ async function getAssignments(session) {
       if (!assignments[splitTestName]) {
         assignments[splitTestName] = []
       }
-      assignments[splitTestName].push({
-        versionNumber,
-        variantName,
-        phase: 'release', // anonymous users can only be exposed to tests in release phase
-        assignedAt,
-      })
+      if (
+        !_.find(assignments[splitTestName], {
+          versionNumber,
+          variantName,
+        })
+      )
+        assignments[splitTestName].push({
+          versionNumber,
+          variantName,
+          phase: 'release', // anonymous users can only be exposed to tests in release phase
+          assignedAt,
+        })
     } catch (error) {
       logger.error(
         { err: error, token },
@@ -193,13 +199,15 @@ async function _convertAnonymousAssignmentsIfNeeded(session) {
       session.sta = ''
     }
     for (const [splitTestName, assignments] of Object.entries(
-      session.splitTests
+      session.splitTests || {}
     )) {
       const splitTest = splitTests.get(splitTestName)
       for (const assignment of assignments) {
         const assignmentString = _buildAssignmentString(splitTest, assignment)
         const separator = session.sta.length > 0 ? TOKEN_SEP : ''
-        session.sta += `${separator}${assignmentString}`
+        if (!session.sta.includes(assignmentString)) {
+          session.sta += `${separator}${assignmentString}`
+        }
       }
     }
     delete session.splitTests
diff --git a/services/web/test/unit/src/SplitTests/SplitTestSessionHandlerTests.js b/services/web/test/unit/src/SplitTests/SplitTestSessionHandlerTests.js
index b9216c8464..ac1159a78d 100644
--- a/services/web/test/unit/src/SplitTests/SplitTestSessionHandlerTests.js
+++ b/services/web/test/unit/src/SplitTests/SplitTestSessionHandlerTests.js
@@ -120,7 +120,7 @@ describe('SplitTestSessionHandler', function () {
     })
   })
 
-  it('should not read from the sta field', async function () {
+  it('should read from the sta field', async function () {
     this.SplitTestCache.get = sinon.stub().resolves(
       new Map(
         Object.entries({
@@ -190,6 +190,76 @@ describe('SplitTestSessionHandler', function () {
     })
   })
 
+  it('should deduplicate entries from the sta field', async function () {
+    this.SplitTestCache.get = sinon.stub().resolves(
+      new Map(
+        Object.entries({
+          'anon-test-1': {
+            _id: '661f92a4669764bb03f73e37',
+            name: 'anon-test-1',
+            versions: [
+              {
+                versionNumber: 1,
+                variants: [
+                  {
+                    name: 'enabled',
+                  },
+                ],
+              },
+            ],
+          },
+          'anon-test-2': {
+            _id: '661f92a9d68ea711d6bf2df4',
+            name: 'anon-test-2',
+            versions: [
+              {
+                versionNumber: 1,
+                variants: [
+                  {
+                    name: 'v-1',
+                  },
+                  {
+                    name: 'v-2',
+                  },
+                ],
+              },
+            ],
+          },
+        })
+      )
+    )
+    const session = {
+      sta: `Zh+SpGaXZLsD9z43_1=d:sbrvs0;Zh+SqdaOpxHWvy30_1=d:sbtqg0;Zh+SqdaOpxHWvy30_1=d:sbtqg0;Zh+SpGaXZLsD9z43_1=d:sbrvs0;Zh+SqdaOpxHWvy30_2=1:sbsi00;Zh+SqdaOpxHWvy30_1=d:sbtqg0`,
+    }
+
+    const assignments =
+      await this.SplitTestSessionHandler.promises.getAssignments(session)
+    expect(assignments).to.deep.equal({
+      'anon-test-1': [
+        {
+          variantName: 'default',
+          versionNumber: 1,
+          phase: 'release',
+          assignedAt: new Date(1712829600000),
+        },
+      ],
+      'anon-test-2': [
+        {
+          variantName: 'default',
+          versionNumber: 1,
+          phase: 'release',
+          assignedAt: new Date(1712916000000),
+        },
+        {
+          variantName: 'v-2',
+          versionNumber: 2,
+          phase: 'release',
+          assignedAt: new Date(1712858400000),
+        },
+      ],
+    })
+  })
+
   it('should merge assignments from both splitTests and sta fields', async function () {
     const session = {
       splitTests: {