diff --git a/app/src/main/java/com/nextcloud/talk/chat/MessageInputFragment.kt b/app/src/main/java/com/nextcloud/talk/chat/MessageInputFragment.kt
index 14607a21057..e7c6cd6a74d 100644
--- a/app/src/main/java/com/nextcloud/talk/chat/MessageInputFragment.kt
+++ b/app/src/main/java/com/nextcloud/talk/chat/MessageInputFragment.kt
@@ -7,7 +7,6 @@
 
 package com.nextcloud.talk.chat
 
-import android.content.res.Resources
 import android.graphics.drawable.ColorDrawable
 import android.graphics.drawable.Drawable
 import android.os.Build
@@ -16,6 +15,7 @@ import android.os.CountDownTimer
 import android.os.SystemClock
 import android.text.Editable
 import android.text.InputFilter
+import android.text.Spanned
 import android.text.TextUtils
 import android.text.TextWatcher
 import android.util.Log
@@ -85,7 +85,7 @@ import kotlinx.coroutines.launch
 import java.util.Objects
 import javax.inject.Inject
 
-@Suppress("LongParameterList", "TooManyFunctions")
+@Suppress("LongParameterList", "TooManyFunctions", "LargeClass")
 @AutoInjector(NextcloudTalkApplication::class)
 class MessageInputFragment : Fragment() {
 
@@ -108,6 +108,19 @@ class MessageInputFragment : Fragment() {
         private const val CONNECTION_ESTABLISHED_ANIM_DURATION: Long = 3000
         private const val FULLY_OPAQUE: Float = 1.0f
         private const val FULLY_TRANSPARENT: Float = 0.0f
+
+        /**
+         * Note: Start index guaranteed >= 0 if correct, -1 if error
+         * @return `Pair(start index + 1, end index)
+         */
+        private fun String.getStartAndEndIndexOf(substring: String): Pair<Int, Int> {
+            val index = this.indexOf(substring)
+            if (index < 0) return Pair(-1, -1)
+
+            val start = kotlin.math.max(0, index + 1)
+            val end = start + substring.length
+            return Pair(start, end)
+        }
     }
 
     @Inject
@@ -156,10 +169,6 @@ class MessageInputFragment : Fragment() {
         saveState()
     }
 
-    override fun onResume() {
-        super.onResume()
-    }
-
     override fun onDestroyView() {
         super.onDestroyView()
         if (mentionAutocomplete != null && mentionAutocomplete!!.isPopupShowing) {
@@ -348,7 +357,7 @@ class MessageInputFragment : Fragment() {
 
                 if (s.length >= lengthFilter) {
                     binding.fragmentMessageInputView.inputEditText?.error = String.format(
-                        Objects.requireNonNull<Resources>(resources).getString(R.string.nc_limit_hit),
+                        Objects.requireNonNull(resources).getString(R.string.nc_limit_hit),
                         lengthFilter.toString()
                     )
                 } else {
@@ -356,27 +365,36 @@ class MessageInputFragment : Fragment() {
                 }
 
                 val editable = binding.fragmentMessageInputView.inputEditText?.editableText
+                if (editable == null || binding.fragmentMessageInputView.inputEditText == null) return
+
+                val mentionSpans = editable.getSpans(
+                    0,
+                    binding.fragmentMessageInputView.inputEditText!!.length(),
+                    Spans.MentionChipSpan::class.java
+                )
+                var mentionSpan: Spans.MentionChipSpan
+                for (i in mentionSpans.indices) {
+                    mentionSpan = mentionSpans[i]
+
+                    val spStart = editable.getSpanStart(mentionSpan)
+                    val spEnd = editable.getSpanEnd(mentionSpan)
+                    val spanRangeStr = editable.subSequence(spStart, spEnd).toString().trim { it <= ' ' }
+                    val error = spanRangeStr.length > mentionSpan.label.length
+
+                    if (start in spStart..<spEnd && spanRangeStr != mentionSpan.label) {
+                        editable.removeSpan(mentionSpan)
+                    }
 
-                if (editable != null && binding.fragmentMessageInputView.inputEditText != null) {
-                    val mentionSpans = editable.getSpans(
-                        0,
-                        binding.fragmentMessageInputView.inputEditText!!.length(),
-                        Spans.MentionChipSpan::class.java
-                    )
-                    var mentionSpan: Spans.MentionChipSpan
-                    for (i in mentionSpans.indices) {
-                        mentionSpan = mentionSpans[i]
-                        if (start >= editable.getSpanStart(mentionSpan) &&
-                            start < editable.getSpanEnd(mentionSpan)
-                        ) {
-                            if (editable.subSequence(
-                                    editable.getSpanStart(mentionSpan),
-                                    editable.getSpanEnd(mentionSpan)
-                                ).toString().trim { it <= ' ' } != mentionSpan.label
-                            ) {
-                                editable.removeSpan(mentionSpan)
-                            }
+                    // workaround, not a proper fix for issue #4642
+                    if (error) {
+                        val pair = spanRangeStr.getStartAndEndIndexOf(mentionSpan.label.toString())
+                        if (pair.first < 0) {
+                            Log.e(TAG, "Mention Span not found in editable: Not reinserted")
+                            return
                         }
+
+                        editable.setSpan(mentionSpan, pair.first, pair.second, Spanned.SPAN_INCLUSIVE_INCLUSIVE)
+                        Log.e(TAG, "Reinserted Span in editable at Start: ${pair.first} End: ${pair.second}")
                     }
                 }
             }
diff --git a/app/src/main/java/com/nextcloud/talk/utils/CharPolicy.java b/app/src/main/java/com/nextcloud/talk/utils/CharPolicy.java
index add1d48d768..baedde6d653 100644
--- a/app/src/main/java/com/nextcloud/talk/utils/CharPolicy.java
+++ b/app/src/main/java/com/nextcloud/talk/utils/CharPolicy.java
@@ -9,12 +9,14 @@
 
 import android.text.Spannable;
 import android.text.Spanned;
-import androidx.annotation.Nullable;
+
 import com.otaliastudios.autocomplete.AutocompletePolicy;
 
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+import androidx.annotation.Nullable;
+
 public class CharPolicy implements AutocompletePolicy {
 
     private final char character;