Test case demonstrating WAL file size growth. Tested on Couchbase.Lite 1.4.0 & 1.4.1

CouchbaseWalIssue.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Couchbase.Lite;
using Couchbase.Lite.Util;

namespace CouchbaseWalIssue
{
    public class Program
    {
        private const string DIRECTORY_PATH = "D:\\CouchbaseWalIssue";
        private const string DB_NAME = "waltest";

        private static Manager manager;
        private static Database db;

        private static void SetupLogger()
        {
            // Basic logger that prints to the Console
            Log.SetLogger(new ConsoleLogger());
            Log.Domains.Database.Level = Log.LogLevel.None;
        }

        private static void Main()
        {
            SetupLogger();
            const string tag = "MAIN (Main)";
            
            manager = new Manager(Directory.CreateDirectory(DIRECTORY_PATH), ManagerOptions.Default);
            db = manager.GetDatabase(DB_NAME);
            Log.I(tag, $"WAL size: {GetWalFileSize() / 1024.0} KB");

            const int newDocsCount = 1000;
            Log.I(tag, $"Adding {newDocsCount} documents..");
            AddDocuments(newDocsCount);
            Log.I(tag, $"Document count: {db.GetDocumentCount()}");
            Log.I(tag, $"WAL size: {GetWalFileSize() / (1024.0*1024.0)} MB");

            const int purgeDocsCount = 500;
            Log.I(tag, $"Purging {purgeDocsCount} documents..");
            PurgeDocuments(purgeDocsCount);
            Log.I(tag, $"Document count: {db.GetDocumentCount()}");
            Log.I(tag, $"WAL size: {GetWalFileSize() / (1024.0*1024.0)} MB");

            Log.I(tag, "Compacting..");
            db.Compact();
            Log.I(tag, $"WAL size: {GetWalFileSize() / (1024.0*1024.0)} MB");

            Log.I(tag, "Closing db..");
            db.Close();
            Log.I(tag, $"WAL size: {GetWalFileSize() / (1024.0*1024.0)} MB");

            Console.WriteLine("Press any key to exit");
            Console.ReadKey();
        }

        private static long GetWalFileSize()
        {
            var walFile = new FileInfo($"{DIRECTORY_PATH}\\{DB_NAME}.cblite2\\db.sqlite3-wal");
            return walFile.Length;
        }

        private static void AddDocuments(int newDocsCount)
        {
            db.RunInTransaction(
                () =>
                {
                    for (var i = 0; i < newDocsCount; i++)
                    {
                        var doc = db.CreateDocument();
                        doc.PutProperties(
                            new Dictionary<string, object>
                            {
                                {"SentTimeStamp", DateTime.Now.ToString("G")},
                                {"SenderId", new string('*', 50)},
                                {"MessageType", new string('*', 50)},
                                {"Payload", new string('*', 1000)}
                            });
                    }
                    return true;
                });
        }

        private static void PurgeDocuments(int purgeDocsCount)
        {
            var docIds = db.CreateAllDocumentsQuery()
                           .Run()
                           .Take(purgeDocsCount)
                           .Select(x => x?.DocumentId);

            foreach (var docId in docIds)
            {
                if (docId == null)
                    return;

                var document = db.GetDocument(docId);
                document.Purge();
            }
        }
    }
}